Question 162164
When you are traveling upstream you are going against the current so you have to overcome the speed of the current which will slow you down.

Rate of motorboat upstream is x-3

When you are traveling downstream the current contributes to your speed

Rate of motorboat downstream x+3

Distance traveled is the same

(x-3)5=(x+3)(2.5)

5x-15=2.5x+7.5

add 15 to both sides 

5x=2.5x +22.5

Subtract 2.5x from both sides

2.5x=22.5

Divide both sides by 2.5

x=9 miles per hour

Let's double check

(9-3)*5=30 

12*2.5=30