Please send help, and explain if you can <333

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.

If f(x)= sqrt4x+9+2, which inequality can be used to find the domain of f(x)?

Why is causation so much more difficult to prove than correlation?