2/5 (y-40) = 5 (solve for y)

First, multiply both sides by 5 to get rid of the faction:

2 (y-40) = 25

then, divide both sides by 2 to get rid of the 2 in the left side:

y-40 = 12.5

then, isolate the y in one side and the other terms on the other.

y = 12.5+40

y = 52.5