X is partly varies as y and as partly as the cube root of y. If x=2 where y=8 and x=3 and y=27.find x when y=81

Answer 1

x = ay+b∛y
So, using your two data points, you can find a and b by solving
8a+2b = 2
27a+3b = 3
That means that a=0, b=1 and
x = ∛y
Seems kind of strange, but if there are no typos, it is what it is.

Answer 2

x^3 = 81
X = 4.3267.