It takes three hours for a boat to go 18 miles downstream, and nine hours to return. What is the rate of the boat in calm water and the rate of the current?

Step-by-step explanation:

Distance = rate * time

If B is the rate of the boat, and C is the rate of the current, then we can write two equations:

18 = (B + C) * 3

18 = (B - C) * 9

Simplifying the equations:

6 = B + C

2 = B - C

Add the equations together to eliminate C:

8 = 2B

B = 4

Plug into either equation to find C:

C = 2

The boat's rate is 4 mph, and the current's rate is 2 mph.