Question 761684
A ferry leaves a harbor and travels to a resort island at an average speed of 20 mph. On the return trip, the ferry travels at an average speed of 10 mph because of fog. The total time for the trip is 6 h. How far is the island from the harbor? 
let t=hrs to reach the island
6-t=hrs for return trip
distance=travel time*speed (same for both directions)
20t=10(6-t)
20t=60-10t
30t=60
t=2
20t=40
How far is the island from the harbor?40 miles