For this case we have the following variables:
d: number of days
c: total number of cars
We know that an amount of 100 cars per day is produced.
Therefore, the equation that models the problem is:

We can write this equation as a function of the number of days.
Therefore, by rewriting the equation we have:

Answer:
An equation that represents the number of cars as a function of the number of days is:

option c