He slept 1/3 of the day, and is awake 2/3 of the day (note that 1/3 + 2/3 = 3/3 = 1)
2/3 of 5/8 = (2/3)*(5/8) = (2*5)/(3*8) = 10/24 = 5/12 of the day is spent at home when he is awake
Add 1/3 and 5/12 to get
1/3 + 5/12 = 4/12 + 5/12 = (4+5)/12 = 9/12 = 3/4
He spent 3/4 of a whole day at home (equivalent to 18 hours)
Answer: 3/4