Question 1154154
Drawing and labeling the figure exactly as described, x being the distance from bottom of ladder to the wall on the ground, 
{{{(x+3)^2+x^2=15^2}}}
and in this case, the question asks for x+3.
(A different assigning of variables is possible.)


Simplifying the equation, you find {{{x(x+3)=108=9*12}}}, and x+3 corresponds to 12 feet up the wall.