Answer:
Option C -

Explanation:
Given : An exercise class had 18 people. If each person produced 1,900 BTUs of body heat during the class and the room is 28 ft × 32 ft × 12 ft.
To find : How many BTUs per cubic foot did they produce?
Solution :
Number of people = 18
BTU produced by each person = 1900
Total BTU produced by 18 persons is given by

Dimension of the room is given by
Length of room = 28 ft
Width of room = 32 ft
Height of room = 12 ft
So, Volume of room is given by



So, Number of BTU's per cubic foot is given by



Therefore, Option C is correct.
3.18 BTUs per cubic foot did they produce.