Answer:
Speed_still = 12.25 mi/h
Speed_current = 1.75 mi/h
Step-by-step explanation:
In the first trip, the motorboat goes upstream
Speed_boat = Speed_still - Speed_stream
The speed is defined as
Speed = Distance / time
This means
Speed_boat = 21 miles/ 2 h = 10.5 mi/h
Then
Speed_still - Speed_stream = 10.5 mi/h
In the second trip:
Speed_boat = Speed_still + Speed_stream
Speed_boat = 21 miles/ 1.5 h = 14 mi/h
Speed_still + Speed_stream = 14 mi/h
Then, the ystem of equations result
Speed_still + Speed_stream = 14 mi/h
Speed_still - Speed_stream = 10.5 mi/h
If we add them together
2*Speed_still = 24.5 mi/h
Speed_still = 12.25 mi/h
Speed_stream = 14 mi/h - 12.25 mi/ h = 1.75 mi/h
