2 boats left the pier in opposite directions. The first boat sailed at a speed of 4 km / h

2 boats left the pier in opposite directions. The first boat sailed at a speed of 4 km / h and the second 5 km / h. Find the time when the distance between them will be 45 km?

First you need to find the speed at which the two boats are traveling, or rather the overall speed.
1) 4 + 5 = 9 (km / h) – the speed of the first and second boats (total speed);
In order to find the time, you need to divide the distance by the total speed, because the boats go in opposite directions:
2) 45: 9 = 5 (h) – the time when the distance between the two boats is 45 km
Answer: 5 hours.