Answer:
10.5 miles
Step-by-step explanation:
Let b represent the distance traveled by boat. The relation between speed, distance, and time is ...
time = distance / speed
We are told the total time and the total distance so we have ...
b/7 + (14-b)/2 = 3.25
2b +7·14 -7·b = 14·3.25 . . . multiply by 14
3.75·14 = 5b . . . . . . . . . . . .add 5b-14·3.25
b = 10.5 . . . . . . . . . . . . . . . divide by 5
They traveled 10.5 miles by boat.
_____
<em>Check</em>
10.5/7 +3.5/2 = 1.5 +1.75 = 3.25 . . . . the answer checks OK
They spent 1.75 hours walking 3.5 miles to the dock and 1.5 hours traveling 10.5 miles by boat.
