Answer:
2
Explanation:
We are given that Total people=60
Number of people ranked vanilla last=

Number of people ranked vanilla before chocolate =

Number of people ranked vanilla before strawberry=

We have to find number of people ranked vanilla first.
Number of people ranked before vanilla first=Number of people ranked before both
Number of people ranked before both=number of people ranked before chocolate+number of people ranked before strawberry+number of people ranked before neither-number of people responded
Number of people ranked before both=36+6+20-60=2
Hence, the number of people ranked vanilla firs=2