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?

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