Part A: You can add the time in hours to find the total. 1/3 + 3/4 + 4/6 + 1/2 = 2 1/4 hours which can also be expressed as 2 hours and 15 minutes (1/4 of an hour is 15 minutes.)
Part B: It takes him 3/4 hr to do homework, 4/6 hr to play soccer, and 1/2 hr to play piano. 3/4 + 4/6 + 1/2 = 1 11/12 hrs or 1 hour and 55 minutes (11/12 of an hour is 55 minutes.) Therefore Kevin is wrong.