Question 154350
First remove all the parentheses, next combine like terms.
{{{(7x^2-x+1)-(2x^2-x-3)-(5x^2+3x-10)}}}

={{{7x^2-x+1-2x^2+x+3-5x^2-3x+10}}}
={{{7x^2-2x^2-5x^2-x+x-3x+1+3+10}}}
={{{-3x+14}}}