Acar servicing station is running a special offer. the breakdown of the cost for different services is given below.

membership fee: $50 (one-time cost)
air freshener cost: $4 per car per month
washing cost: $10 per car per month
tire replacement cost: $400 per car
tire pressure check cost: $15 per month
the total cost for 12 months of this service for n cars is given by the expression below.

568n+230

which statement best describes the constant in the expression?

a.
it is the total cost of the air freshener, washing, and tire replacement for 12 months.
b.
it is the total cost of the membership fee and the tire pressure check for 12 months.
c.
it is the monthly cost of the membership fee and the tire pressure check.
d.
it is the monthly cost of the air freshener, washing, and tire replacement.