You can Google up ways to market Indie books.
You can spend a few hours each night for a few weeks reading through these threads and get ideas.
You can take the time to create social media profiles for your book and promote them.
You can take out ads for your book in media where you might find your target audience/buyers.
You can do free promotions to try and get some positive reviews, though they work better with the first book of a series.
Keep in mind, for the vast majority of indie authors, paid advertising rarely results in more sales than the advertising cost.
Thinking of a story is easy. Writing it isn't that difficult. Making it believable is difficult as the devil can be in the details. Editing it so that it is great to read is hard for the majority of writers. Promoting it is definitely the hardest part of all and can be very disheartening. Study, learn, keep writing, keep promoting - we need more children's books about the importance of maths, science and learning.
You're asking $10 for the Kindle version (yes, I know it's in Select, too), which is pretty high. And I see you did your own illustrations, but frankly, the cover looks very amateurish. Both these things are going to put off potential buyers, in my opinion, no matter where you advertise.
Think you need to make your character Bryan much more interesting from the start. Most children I've come across, including my own when young, and latterly my grandchildren, would not immediately warm to an outsider boy who was a smart wotsit at mathematics. Maybe if he joined in playing hopscotch with the children to start with. Got some rapport with them, and gradually it unfolded he was a whizz with sums. Children like to feel included with good guys, or boo the baddie. Distinction needs to be made clear at an early stage. It's hard enough to engage most adults swiftly in a narrative, let alone youngsters. And the writing is in a clunky adult style. See the story as a child, not an adult. My opinion only, but I'd address that before spending money on advertising. Also over ten dollars is way too high for 93 pages if it isn't illustrated.
It's illustrated with the author's own pencil drawings. Though I think the one with granny needs to have her do something rather than stand tall, vertically crooked, and do nothing except occupy the far left corner of the book area.
The smart wotsits might enjoy the story? I agree if you are trying to engage kids in math, throwing a math genius in as the protagonist isn't going to seem appealing to kids that have trouble with math. I liked math but even I would revolt at being forced to read a book trying to blatantly teach me something. :P
I take it, from the fact that you've tried to remove the post title and content, that you don't have the thick skin I warned you that you'd need. Too late for that, my friend, once others have started to respond and quoted your original post.
It would have been more gracious to simply thank everyone for their advice and tell them you would take it all under advisement, rather than try and shut people down from adding further comments by removing your post. All you've done now is attracted more people to your thread, wondering what on earth 'none' is all about.