Answer:
a. The number of seniors that went on the trip is 15;

b. The number of seniors that did not go on the field trip is 3;

c. There is not enough information to solve this question.
Step-by-step explanation:
Given that "Of the 18 seniors in her class , 5/6 went on a trip"
a. The number of seniors that went on the trip is;

So, the number of seniors that went on the trip is 15;

b. The number of seniors that did not go on the field trip is;

So, the number of seniors that did not go on the field trip is 3;

c. the number of students from the class that did not go on the field trip.
There is not enough information to solve this question.