Answer:
The speed of the boat in still water is 30 mph, and the speed of the current is 6 mph.
Step-by-step explanation:
Let's say b is the speed of the boat in still water, and c is the speed of the current.
Distance = rate × time
Going downstream:
504 = (b + c) × 14
36 = b + c
Going upstream:
504 = (b − c) × 21
24 = b − c
Two equations, two variables. Solve with substitution or elimination. To use elimination, add the equations together.
60 = 2b
b = 30
Plug into any equation to find c.
36 = b + c
36 = 30 + c
c = 6
The speed of the boat in still water is 30 mph, and the speed of the current is 6 mph.
