Answer:
36 Crew members
Explanation:
Divide 540 by 15, to find how much the new amount of passengers had increased. It should be 36.
Now to keep the ration even, you need to multiply the amount of Crew members by 36 too.
Double checking your answer:
1/15=0.06666666667...
36/540=0.06666666667...
There's probably other ways to solve this, this is just how I did it.