Four classes A, B. C and D raised money for a charity. Classes A and B raised a total of $108. Together, classes B, C and D raised a total of $180. The total amount of money raised by all 4 classes is 5 times the amount that class B raised. How much money did class B raise?
a+b = 108
b+c+d = 180
a+b+c+d = 5b
solve to get b=48