Desribe the measurements necessary to find the average speed of a high school track athlete

You only need to measure the distance the athlete covered and the time it takes for him to run that distance. Average speed is calculated as distance/time, in whatever units you prefer. Since speed is a scalar, it's different with velocity, which is a vector, meaning you have to take the direction into account. To calculate the average speed, you don't have to know in which direction the athlete runs, but just the distance and time.