The answer must be greater than 7, else the two sides are less than or equal to the third. That triangle is impossible. The answer must also be less than 34, because then the two other sides would equal the third, making an impossible triangle.
We can start by separating the x^3, and that means we have to multiply both sides by 4, resulting in x^3=27. Next, we can find the cube root of both sides ( as x is the cube root of x^3), getting x=3