2 choices:

1. Take the M60 into Manhattan to the Lexington Ave stop. Take the 6 downtown to 77th Street. He can then walk 2 blocks uptown and 4 blocks east to 79th & York.

If he wants, when he gets to 79th St., he can hop on the M79 bus to York Ave but by doing that, he'll be charged an extra metrocard fare. That's up to him. If it's pouring outside, he might want to do that if he can't find a taxi at 77th & Lex. The blocks east are longer than the ones uptown/downtown. It's not a big deal to me, but if he's got a lot of luggage, it might be.

2. Take the M60 into Manhattan and get off at 2nd Ave. He can then walk 1 block to 126th Street and catch the M15 bus to 79th Street. By doing this, his walk to 79th and York is easily halved.