The first barn contained 3 times more hay than the second one. after 20 tons of hay were removed from the first barn and 20 tons were added to the second barn, the amount of hay in the second barn was 5/7 of the amount remaining in the first barn. how many tons of hay was there in each barn?

The solution would be like this for this specific problem:

a + 20 = 5/7 (3a - 20) 
a + 20 = (15a - 100)/7 
Multiply both side by 7, 
7a + 140 = 15a - 100 
8a = 240 
a = 30

3a = 90

a + 20 = 50

3a - 20 = 70

c.

step-by-step explanation:

because first you have to add the 4x, 9x, and the 7x together and you get 20x and then you add the last numbers up and you get 5and then you put the subtraction sign in there and that's how you get the answer.