Task: Question Answering
Input (English): Problem: the average mark of the students of a class in a particular exam is 80. if 5 students whose average mark in that exam is 60 are excluded, the average mark of the remaining will be 90. find the number of students who wrote the exam.
Options: a. 22, b. 27, c. 15, d. 99, e. 21
Output (English): c