H=xW/x-8s
$\displaystyle H=\frac{xW}{x-8s} $
Multiplying both sides by x -8s we get:
$\displaystyle H(x-8s)=xW $
$\displaystyle Hx - 8Hs = xW $
If we subtract xW from both sides we get all the terms containing x on the left hand side:
$\displaystyle Hx - xW -8Hs = 0$
Adding 8Hs to both sides:
$\displaystyle Hx - xW = 8Hs $
Factorising the left hand side:
$\displaystyle x(h-W) = 8Hs $
And dividing both sides by (h-w) gives the result:
$\displaystyle x=\frac{8Hs}{h-w} $