Question

f + g = h, solve for g; f - h = g; h - f = g; hf = g; h + f = g

Explanation:

Step1: Isolate g

Subtract f from both sides of the equation $f + g=h$.
$f + g - f=h - f$

Step2: Simplify

$g=h - f$

Answer:

$h - f = g$ (the second option in the image)