Concept: The question tests on the basic concepts of Set theory

Solution: 
Let the total number of Students = x

Total = A + B - (A ∩ B) + (A U B)'

Total = Students who passed in Math + Students who passed in Science - Students who passed in both + Students who failed in both.

x = 0.7x + 0.75x - 0.65x + 60

x + 0.65x - 0.7x - 0.75x = 60

0.2x = 60

x = 300

Option C