Question 1036538
hint means simple distribution or multiplying
{{{x^2+7x=12+8x}}} gather everything on left side so subtract 12 and 8x from both sides
{{{x^2+7x-8x-12=0}}}
{{{x^2-x-12=0}}}

several ways to solve this i chose the fast way which is finding two numbers that multiply to get -12 and add to get -1 these numbers come from: find 2 numbers that multiply to get c and add to get b in the quadratic equation formula {{{ax^2+bx+c=0}}} 

a {{{-4}}} and a {{{3}}} multiply to {{{-12}}} and add to {{{-1}}}
{{{(x-4)(x+3)=0}}}
x= 4 , -3
if you cant get that trick down just do the long quadratic equation:

*[invoke quadratic "x", 1, -1, -12 ]