1/10 = 1/120 * 12
and we know that you can move a constant outside of the integral
1/120 ∫12x(6x^2-15) dx
=1/120 ∫ 72x^3-180x dx
I'm sorry i forgot that it was possible that you didn't cover u-substitution, which is just a method of integration and all you had to do was multiply it out and integrate the polynomial! sorry!
and 1/120 was probably to avoid fractions during integration