Answer:
A. n represents the number of members, so it must be a whole number.
Explanation:
Since 12.125 is a decimal, it would not make sense to substitute 12.125 for n in the expression. You cannot have 1/8 of a person. Since each member is contributing an additional $5, the expression will show n as the variable representing the number of members in the Math Club. Each member is giving 5, so 5n + 10, the 10 being the coupon they have for $10 off. This expression shows how much money the entire group has.