Final answer:
The equation A = GH shows that A varies jointly with G and H, and can be solved for G by rearranging it to G = A/H.
Step-by-step explanation:
The student has asked about an equation that expresses a joint variation relation where A varies jointly as G and H. The correct equation representing this relationship is A = GH, meaning that A varies directly with both G and H. To solve for G, we rearrange the equation to isolate G, resulting in G = A/H. The variation equation shows how when two variables are directly proportional to each other while keeping a third variable constant, their product is constant.