The distance between two piers on a river is 45 miles. It takes a motorboat, moving downriver, 2 hr 15 min to complete the journey. How much time does it take the same boat to go back upstream if the current flows at 2.5 mph?

Answer: 3 hours

Step-by-step explanation: we can make a variable for our answer (x)

Now, we need to find the speed of the boat without the current (y)

we can make this equation: d/t = s: 45 / (y + 2.5) = 2 1/4

hence: y = 17.5

now we can substitute in the current's speed: y - 2.5

17.5 - 2.5 is 15

now we can solve for x

45/15 = 3

hence, we get 3 hours as our answer