A is smaller by 1/5 of b
So if you add a and 1/5 of b you would have b:
a + 1/5b = b
Solving for a you have:
A = b - 1/5b = 4/5b
A = 4/5b
Solving for b divide both sides by 4/5:
B = 5/4a
Since 4/4 = 1, this means b I’d bigger than a by 1/4
The answer = 1/4