The area of a poster board is (x2 + 9x − 10) square inches. Find the dimensions of the poster board if x = 13. The dimensions of the poster board are |

I asume you mean ${x}^{2}+9x-10$, so I will go with that.

${x}^{2}+9x-10$

Subsitute $x$ for 13.

${13}^{2}+9\times13-10$

$169+9\times13-10$

$169+117-10$

$286-10$

$276$

x² - 9x + 10 can be factored as (x - 1)*(x + 10) so the side lengths will be x-1 (= 12 in²) and x+10 (=23in²)