Xiao Gang started from home, crossed the top of the mountain and went to grandma's home at the foot of the mountain. He walked 19.5 kilometers. He walked 3 kilometers an hour up the mountain and 5 kilometers an hour down the mountain. He started at 5 in the morning and arrived at Grandma's home at 10:30. After playing at Grandma's home for two hours, he returned at the same speed. What time was Xiao Gang back home in the afternoon?
Starting from 5 in the morning, it was exactly 10:30 to grandma's house, which took 4.5 hours
If the uphill distance is x km, the downhill distance is (19.5-x) km,
X÷3+(19.5-X)÷5=4.5
X=4.5
It takes 4.5 △ 5 + (19.5-4.5) △ 3 = 5.9 hours to return at the original speed, so after playing at Grandma's house for two hours, Xiao Gang returns home at 6:24 p.m