Question 896702
If that number is x...

{{{x^2 + 3x = 108}}}

{{{x^2 + 3x - 108 = 0}}}

{{{x = (-3 +- sqrt(9 + 4*108))/2}}}

{{{x = (-3 +- 21)/2}}}

{{{x = 9}}} or {{{x = -12}}}

I used the formula {{{x = (-b +- sqrt(b^2-4*a*c ))/(2*a) }}}