Answer: 
Step-by-step explanation:
Knowing the information provided in the exercise, you need to find the Least Common Multiple (L.C.M) in order to solve it.
You can follow these steps:
1- You must descompose 2, 5 and 8 into their prime factors:

2- And finally, you must multiply the commons and non commons with the highest exponent:

Therefore, the answer is: 
So, the first thing you want to find out is how many seconds each person adds to the wait time. Find out how many seconds are in 20 minutes.. 20*60=120. 120/150=0.8 seconds. Each person adds 0.8 seconds to the wait time. Now, multiply that by 240.. 240*0.8=192 seconds. Lastly, find out how many minutes 192 seconds is... 192/60=32 minutes.
I hope I did that right! And if I did, I hope that helped!
Your answer would be 8 Hammond per minute. Hope this helps!
I'm not sure but I'm gonna guess that the answer is 50?