Arturo O. answered 06/07/20
Experienced Physics Teacher for Physics Tutoring
The person who gave you that answer "lost" the y3 in the numerator!
(x1/2 y / y1/2)3 = (x1/2 y)3 / ( y1/2)3 = x3/2y3 / y3/2 = x3/2 y3-3/2 = x3/2y6/2-3/2 = x3/2y3/2 = (xy)3/2