7 students took only religion .
We can solve this problem without using a formula.
We are given the following information:
Total students = 135
English only = 16
Math and religion = 11
English and religion = 12
All three = 6
We can calculate the number of students who took only religion by subtracting the number of students who took religion in combination with other subjects from the total number of students who took religion:
Students taking religion = 36
Students taking religion only = students_taking_religion - (math_and_religion + english_and_religion + all_three)
Students taking religion only = 36 - (11 + 12 + 6)
Students taking religion only = 7
Therefore, 7 students took only religion.