10x^2 - (2x - 3)(5x - 1) = 31;

10x^2 - (10x^2 - 2x - 15x + 3) = 31;

10x^2 - 10x^2 + 2x + 15x - 3 = 31;

2x + 15x = 31 + 3;

17x = 34;

x = 34 : 17;

x = 2.