Jack and Gary started jogging from the same spot in opposite directions along a straight path. Both of them jogged for 3/4h. They were 15 km apart in the end. Given that Jack's average speed was 12 km/h, what was Gary's average speed in km/h?
12 * (3/4) = 9
Jack is 9 km apart from the initial position, which means Gary must be 6 km apart from the original position.
6/3 * 4 = 8.
Gary is travelling at 8 km/h