Sa=2(1h)+2(1w)+2(hw)

Solution for Sa=2(1h)+2(1w)+2(hw) equation:

Simplifying
Sa = 2(1h) + 2(1w) + 2(hw)

Remove parenthesis around (1h)
aS = 2 * 1h + 2(1w) + 2(hw)

Multiply 2 * 1
aS = 2h + 2(1w) + 2(hw)

Remove parenthesis around (1w)
aS = 2h + 2 * 1w + 2(hw)

Multiply 2 * 1
aS = 2h + 2w + 2(hw)

Reorder the terms:
aS = 2h + 2hw + 2w

Solving
aS = 2h + 2hw + 2w

Solving for variable 'a'.

Move all terms containing a to the left, all other terms to the right.

Divide each side by 'S'.
a = 2hS-1 + 2hwS-1 + 2wS-1

Simplifying
a = 2hS-1 + 2hwS-1 + 2wS-1