From two villages, the distance between which is 9 km, two riders simultaneously rode in one direction

From two villages, the distance between which is 9 km, two riders simultaneously rode in one direction in front of the rider galloping at a speed of 7 km / 4 hours after the start of the movement, his speed of the second rider

1) When moving against the current, the speed of the river is subtracted from the speed of the steamer, therefore, its own speed will be:

28 + 18 = 46 km / h.

When moving downstream, the current speed should be added to its own speed:

46 + 18 = 64 km / h.

2) In 4 hours, the first rider covered the distance:

7 * 4 = 28 km.

Consequently, the second one overcame during the same time:

9 + 28 = 37 km.

Then his speed was:

37: 4 = 9.25 km / h.

Answer: the speed of the second rider is 9.25 km / h.