Gaining

Weight gain in 3 weeks

Well purely from a math stand point he'll need like 2000 extra calories a day to pull it off, so maybe go check out some of the gain shake recipes on here is probably a good start.

As always, i'm going to recommend a bit of moderation in junk food. Burgers may be cheap and calorie dense but all that grease is going to wreck your stomach and isn't good for you in the long run. Honestly, huge portions of what he eats now is probably the best advice.
9 years