Problem: (5x^4 - 3x^3 + 6x) - (3x^3 + 11x^2 - 8x)

Answer: 5x^4-6x^3 - 11x^2 + 14x

Combine the like terms by adding the coefficients,

->5x^4 can't add anything so leave it there,

->-3x^3 can add - 3x^3 which gives you - 6x^3,

->We can't do anything with - 11x^2 so leave it there as well,

->6x add to - (-8x) gives you 14x,

You will get for your final answer is 5x^4-6x^3-11x^2+14x.