Question 64381
First, get your equation into the standard form for quadratic equations: {{{ax^2 + bx + c = 0}}}
{{{3x = 18-x^2}}} Add {{{x^2}}} to both sides of the equation.
{{{x^2 + 3x = 18}}} Now subtract 18 from both sides.
{{{x^2 + 3x - 18 = 0}}} Factor this quadratic equation.
{{{(x + 6)(x - 3) = 0}}} Apply the zero product principle.
{{{(x+6) = 0}}} and/or {{{(x-3) = 0}}}
If {{{(x+6) = 0}}} then {{{x = -6}}}
If {{{(x - 3) = 0}}} then {{{x = 3}}}

The solutions:
{{{x = -6}}}
{{{x = 3}}}