Researchers at a university designed and tested a​ speed-training program for junior varsity and varsity high school football players. Each in a sample of 38 high school athletes was timed in a​ 40-yard sprint prior to the start of the training program and timed again after completing the program. The decreases in times​ (measured in​ seconds) are listed in the accompanying table.​ [Note: A negative decrease implies that the​ athlete's time after completion of the program was higher than his time prior to​ training.] The goal of the research is to demonstrate that the training program is effective in improving​ 40-yard sprint times. Use these data to complete parts a and b below.