The Manager of a Pharmaceutical Sales Team in Mumbai Wishes

The manager of a pharmaceutical sales team in Mumbai wishes to calculate the total expenses (y) of his team. Expenses may be in three categories: travel (t) ; food (f) and accommodation (a) . Which of the following models is suitable for calculating the value of y?

A) y = t x f x a
B) y = t + f + a
C) y = t + f x a
D) y = t x f + a