Don't. My older brother prefers to help me only in some parts I don't get. When I can't understand something, he makes sure I do by repeating it again and again until I do.
I don't know the relationship you guys have, but I'd let him do it himself.
He's my younger brother. I'm the eldest so I am told by our mother to help answer his modules. The two of us (mom and I) answer his modules since he says he's tired, its hard to answer and so on. The only job he has is to write the answers. That's all he had to do while I have to answer my modules and help around the house meanwhile mother makes money and returns home every night to answer his.
I don't know the relationship you guys have, but I'd let him do it himself.