Subtract the cubes: 5(3x^2h+...) the dots represent higher powers of h which will be ignored as h approaches 0;
subtract the squares: 2(2xh+...); the constant 7 cancels out. Total is 15x^2h+4xh, divided by h is 15x^2+4x or x(15x+4). This is the result as approaches 0.