In linear equations, the slope (or rate of change) is represented by m in the next equation:
y = mx + b [1]
We have to remember that b is the intercept at y when x = 0.
Considering that the tire manufacturing plant produces 500 tires a day, and this "tells" us that is this is a rate of change, we can say that the function should be (that is, the function that represents the number of tires produced over x days):
f(x) = 500x
This function "tells" us also that when the production started, x = 0, there were no tires (b = 0).
To check this, we can imagine that every day we produce 500 tires; the next day, another 500 tires, and so on.
Thus, over 2 days, we have that the number of tires produced over 2 days is:
f(2) = 500*(2) = 1000 tires
Over three days:
f(3) = 500*(3) = 1500 tires.
And so forth.
Then, the equation that best models the function that represents the number of tires produced over x days is option C, f(x) = 500x.