Sandy sold half of her comic books and then bought 9 more. she now has 12. how many did she begin with write an equation and solve. me

Sandy began with a number of books that we don't know. Since that number is unknown to us, we use a variable to represent it. Let x = the number of books Sandy began with.

Sandy sold half of her comic books.

She sold x/2 books, and she kept x/2 books.

She kept x/2 books. Then she bought 9 books.

Now she has x/2 + 9 books. We are told she now has 12 books.

That means x/2 + 9 must equal 12. That gives us the equation.

Now we solve the equation. We subtract 9 from both sides.

Multiply both sides by 2.

Since we let x equal the number of books she began with, now we know she began with 6 books.

She began with 6 books.

47 - 90 = 43

43 - 180 = x

x = 137