A school bus starts from the bus stop and travels a distance of 806 m to pick up Maya. After picking up Maya it travels a distance of 720 m to reach Ravi’s stop. The bus now travels a distance of 924 m to reach Janvi's stop. After Janvi’s stop bus travels at a distance of 750 m to reach Aryan's stop. Now the bus travels 1000 m eventually reaching school. What is the average speed of the school bus if the total time taken to reach the school from the bus stop is 20 minutes?