A boat has a speed of 9 miles per hour in calm water. It takes the boat 4 hours to travel upstream but only 2 hours to travel the same distance downstream. Which equation can be used to find c, the speed of the current in miles per hour?

Question

Mercury · Answer

I can't find the answer choices, but I'll attempt to create the equations

in general, d = rt, where d = distance, r = speed or rate, and t = time

we can create one upstream d = rt equation and one downstream d = rt equation

let's assign a variable to the speed of the boat (let's say b) and one variable for the speed of the current (the problem uses c, so we'll use c)

b + c is the speed of the boat downstream (the current makes the boat faster)
b - c is the speed of the boat upstream (the current makes the boat slower)

you have the speeds now, plus the times already given, so you can create both equations for d.

if there's only one equation in the final answer, there's a good chance that the distance equations are being set equal to each other, since the distance is the same both ways

Mercury · Answer

I know this is a lot, but please review it line by line and let me know if/where you get stuck