Memorize the quadratic formula, or else learn the method of completing the square.
General form of a quadratic equation:
\(\displaystyle ax^2+bx+c=0\)
Solve for x, by completing the square (I'll spare you the details). The following is known as the quadratic formula:
\(\displaystyle \boxed{x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}}\)
Now "plug and chug" as Galactus told you.
In the equation \(\displaystyle x^2+7x-36=0\),
\(\displaystyle a=1, b=7, c= -36\)