if y^3/4=5^3, y=?

Im guessing you mean y^(3/4) = 5^3

So then

y^(3/4) = 5^3
y^(3/4) = 125
(3/4)th root of 125 = 625 --> so A

If you mean (y^3)/4 = 5^3 then
the answer is 3.15 (rounded), but I thought that was not what you meant, Its a strange answer.

y(1/4) = 5
y = 5^4
y = 625
OPTION a)

y^(3/4) = 5^3
y = 5^(3 * 4/3)
y = 5^(12/3)
y = 5^4
y = 625

y^3/4=5^3
=> y^1/4 = 5
=> y = 5^4
=> y = 25^2
=> y = 625

(Y^3/4)^4/3 = (5^3)^4/3

y = 125^4/3

y = 625

y^0.75 = 125 so y = 625

its 625