Question 838535
120 less than the square of a number is the same as twice the number 

{{{-120 + x^2 = 2x }}}
add -2x to each side
{{{ x^2 -2x -120  = 0 }}}
We can factor
{{{ (x - 12)(x + 10) = 0 }}}
Possible values for x are 12 and -10
For 12 , {{{-120 + (12)^2 = 2(12)}}}
{{{-120 + 144 = 24}}}
This looks good so 12 works.