Question 1148506
From your diagram,
let h=AC=DC
let x=BC
and then  45-x=CE.


Two right triangles.  You want to find BC, or x.


{{{system(18^2+x^2=h^2,(45-x)^2+20^2=h^2)}}}


{{{18^2+x^2=(45-x)^2+20^2}}}------------simplify and solve for x.