Simplifying by the binomial theorem, we get
x^3 + 12x^2 + 48x + 64 + x^3 + 15x^2 + 75x +125 = x^3 + 21x^2 + 147x + 343 + x^3 - 6x^2 + 12x - 8
Subtract out the x^3 terms....simplify the rest
27x^2 + 123x + 189 = 15x^2 + 159x + 335
12x^2 -36x - 146 = 0 divide through by 2
6x^2 -18x - 73 = 0
Using the Quadratic Formula the two solutions are x ≈ -2.2969 or x ≈ 5.2969