Question 317087
Yeah, use Distance formula D=VT, but isolate it for T: T=D/V


Because the times are the same, you can set the upstream time and downstream time equal to each other. Using Dup and Vup for upstream, and Ddown and Vdown for downstream, we know that Vup = V - 3, and Vdown = V + 3 (you subtract the current when you go against it, and add the current when it helps you):


Dup/Vup = Ddown / Vdown

6/V-3 = 10/V+3


Cross multiply and solve for V, the boat's still water velocity:

6(V+3) = 10(V-3)
6V + 18 = 10V - 30
48 = 4V
V = 12


The boat's speed in still water is 12mph.