What was the population of Springfield after the move?

Question

I don't get how to setup an equation to solve this problem. 

 

Centerville and Springfield had the same population until 30 people moved from centerville to Springfield. After the move, Centerville had 5/6 of the population of Springfield. What was the population of Springfield after the move?

Answer 1

C = Centerville population

S = Springfield population

 

C = S

C - 30 = 5/6(S + 30)

                                  Substitute S for C

S - 30 = 5/6(s + 30)

6(S - 30) = 5(S + 30)

6S - 180 = 5S + 150

S = 330

 

After the move Springfield had 360 people.