A man rows downstream at 35 km/h and rows upstream at 25 km/h. At what speed can he row in still water?

Qustion: A man rows downstream at 35 km/h and rows upstream at 25 km/h. At what speed can he row in still water?

Solution:
Given,
Man rows downstream = 35 km/h
Man rows upstream = 25 km/h
We know that,
Speed in still water = (Downstream speed + Upstream speed​) ÷ 2
= (35 + 25) ÷ 2
= 60 ÷ 2
= 30 km/h