I don't know if you still need help. but the answer is the first one.
3(12)/10(12) + 7(10)/12(10) = 36/120 + 70/120
==> 18/60 + 35/60 = 53/60
A = 7x, c = 4x, s = 3x
a = s+52
7x = 3x+52
4x = 52
x = 13
c = 4x = 52
Caroline gets 52.
Answer 6 hours
Reason
7x + 9.50 = 55
-9.50. -9.50 subtract from both sides
_____________
7x = 45.50
Divide both sides by 7 to isolate x
X = 6.5
So he can rent for 6 hours (the .5 would be charged as a full hour per the problem)
