S = lw +2h +lh, solve for w

S = lw +2h +lh, solve for w

Place lw on the left.
-lw = 2h + 1h - S
combine h terms.
-lw = 3h - S
multiply through by -1.
lw = -3h + S
solve for w.
w = (-3h + S)/l
check my work.