Is the sample valid? what percent of students prefer caramel popcorn?

Is the sample valid?
 First you must see if the number of students in the table corresponds to the number of students surveyed that was 75.
 We have then:
 33 + 15 + 27 = 75
 We have then that:
 The sample is valid.

 what percent of students prefer caramel popcorn? 
 We can make the following rule of three to answer this question:
 75 ---> 100%
 27 ---> x
 Clearing x we have:
 x = (27/75) * (100)
 x = 36%
 36% percent of students prefer caramel popcorn

Ineed with this same question!