Answer:

Step-by-step explanation:
As we move from San Antonio to Houston
let the distance is "d" from Antonio to Houston
Half the time it moves with 54 km/h and next half the time it moves 118 km/h
so we will have


so total time is

now while his return journey half the distance he move with 54 km/h and next half distance with speed 118 km/h
so we have time of return journey

so now we have

now for the average speed we know that


