Question 52812
The trick to this is only combining like terms.  Like terms have the exact same variables with the exact same powers.
{{{(x^3-5x^2-x+4)+(2x^3+7x^2-2x)}}}
{{{(1+2)x^3+(-5+7)x^2+(-1-2)x+4}}}
{{{3x^3+2x^2-3x+4}}}