The distance along the river between points A and B is 45 km. At the same time, two motor boats came

The distance along the river between points A and B is 45 km. At the same time, two motor boats came out to meet each other, their own speeds are equal. After 1.5 hours, they met. Find your own boat speed if the river speed is 3 km / h.

Let us designate the boats’ own speed as x. Then the final speed of the boat, which was floating with the current, will be x + 3, and that of the one that was swimming against the current: x – 3. Knowing the distance and the time spent on the road until the moment of meeting, we make the equations:

1.5 (x + 3) + 1.5 (x – 3) = 45.

1.5x + 4.5 + 1.5x – 4.5 = 45.

3x = 45.

x = 15 (km / h).

Answer: B. The boats’ own speed is 15 km / h.