Answer:
36 passengers
Step-by-step explanation:
Maria averages 20 passengers every 20 minutes, so she places 1 passenger per minute.
Sal averages 20 passengers every 25 minutes, so he places 0.8 passenger per minute.
If they work together, they can place (1 + 0.8) passengers = 1.8 passengers per minute.
In 20 minutes, they can load
1.8 passengers/minute * 20 minutes = 36 passengers