Question 1010990
let
the length of the ladder be {{{c}}} 
the distance from the ground to the top of the ladder  {{{a}}}
 the distance from the bottom of the ladder to the building  {{{b}}}


if the distance from the ground to the top of the ladder is {{{a}}} is{{{9ft}}} less than the length of the ladder {{{c}}}, we have
 {{{a=c-9ft}}}

if the distance from the bottom of the ladder to the building is {{{b=15ft}}}, we have 

{{{c^2=a^2+b^2}}}

{{{c^2=(c-9)^2+(15)^2}}}

{{{c^2=c^2-18c+81+225}}}

{{{cross(c^2)0=cross(c^2)-18c+306}}}

{{{18c=306}}}

{{{c=306/18}}}

{{{c=17}}}