If you were in charge of buying milk for a family of five, but not everyone has breakfast at home every day, what kind of expense would the milk be?

Variable expense

Explanation:

the milk becomes a variable expense because it doesn't have a fixed amount. it could be 2 or 3 or 4 or 1 depending on the number of persons having breakfast everyday over the course of the week but not 5.

if 5 milks are purchased day-in, day-out, the milk would be  afixed expense but that isnt the case here.

the term variable expense ffrom the name means an expense that changes or varies from time to time  

Cheers.

b would have to be the answer