The solution set for -18 x 3 x

Marco has $38.43 dollars in his checking account. his checking account is linked to his amazon music account so he can buy music. the songs he purchases cost $1.29. part 1: write an expression to describe the amount of money in his checking account in relationship to the number of songs he purchases. part 2: describe what the variable represents in this situation.

I'm confused on this could anyone me and show me what i need to do to solve it.

Factor and solve to find roots x squared -x - 90 =0