8x3y-9(x is raised to the third and y is raised to -9. the whole question is encased in a square root symbol with a little 9 in between the signs edges.
Are you sure that is a little 9 and not a little 3 in the radical sign?
The ninth root of 8 x^3 y^-9 is
2^(1/3) x^(1/3) y
The cube root is 2x/y^3
x^(1/3) means "cube root of x"