Concept:The question tests on the basics of framing equations and solving them.
M students received 3 sandwiches
->Every student received 3/m sandwich.
The fourth sandwich was shared b/w (m-4) students.
Each student received 1 / (m-4) sandwich.
Carol has consumed the sandwich at both cases and hence she has consumed
3/m + 1/ (m-4) [These fractions represent sandwich consumed by 1 student ]
=3(m-4) + m / m (m-4)
=3m -12 + m / m (m – 4)
4m - 12 / m (m-4) option (e)