a) You run 100 meters at a speed of 5 meters/sec and then walk 100 meters at 1 meter/sec.

b) You run for 100 seconds at a speed of 5 meters/sec and then walk for 100 seconds at a speed of 1 meter/sec.

For each of these you need to calculate the total distance covered and divide by the total time taken. For example in (a) the time taken for the first leg is 100m/(5 m/s) = 20 seconds, and the second leg is 100m/(1m/s) = 100 seconds, for a total of 120 seconds. Divide that into the total distance covered to find the average speed. Post back with what you get for answers and we'll check it for you.