Answer :
What I did was convert 10km into meters which is 10,000m.Then plugged the rest of the numbers into the average speedequation and solved for (t) to get the seconds for bothrunners finishing the course and then subtracted the 50 year oldstime from the 18 year olds time to get the seconds that the 18 yearold must start after the 50 year old starts running. Which was 209 seconds.