D. 50 mph
Going upstream takes longer because of the flow of the water
Find 
using Pythagorean Theorem,
.
.
.
Hope this helps.
1. It is easier to apply it to real-world situations once you have learned to construct geometric figures using compasses and straightedges.
2. Constructing geometric figures yourself also helps you understand the material and learn easily.
3. There is more accuracy and it is easier to prove your accuracy in your own constructions.
I hope this helps :)
