Perhaps you want to rearrange the equation to solve for length (l).

A = 2(lw + lh + wh) (the equation with 2 factored out)

A/2 = lw + lh + wh (divide by 2)

A/2 - wh = l(w + h) (subtract from the right everything not containing L)

A = 2(lw + lh + wh) (the equation with 2 factored out)

A/2 = lw + lh + wh (divide by 2)

A/2 - wh = l(w + h) (subtract from the right everything not containing L)

**(A/2 - wh)/(w + h) = l**(divide by the coefficient of L)