I am pretty sure that the solution I attach below is the correct one :[tex]ay+ac=by-bc
ay-by=-ac-bc
y(a-b)=c(a-b)[/tex]
[tex]y=c(a-b)/(a-b)
y=c[/tex]
And what about the next part of your task, the answer is :
[tex]A=lw+wh+lh
w=(A-Ih)/(l+h)[/tex]
Do hope you will find it useful!