Help pls i'm really bad at geometry

Need this asap if anyone can i would be very grateful. if you could show workings that would really

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.

Explain how you can use the associative property to evaluate (7x50)x4.