Ask yourself: If the ride were 0 miles long, what would the equation give for $C$? What does that cost represent in the situation?

Once you know what the cost is at 0 miles, decide which choice describes that idea in words.

In Desmos, type y = 4.50 + 2.25x. Treat $x$ as the number of miles and $y$ as the total cost.

Look at where the line crosses the y-axis (this happens when $x = 0$). Note the y-value at this point; that is the cost when 0 miles are driven.

Ask: In the taxi context, what does that y-value at $x = 0$ tell you about the charge for a ride with no miles driven?

The cost equation is

There are two parts:

• $4.50$: a constant term (does not change with $m$)
• $2.25m$: a term that depends on $m$, the number of miles

The constant term usually represents the starting amount when the variable (here, $m$) is $0$.

To understand the meaning of $4.50$, set $m = 0$ (no miles driven):

So when the customer rides $0$ miles, the cost $C$ is $4.50$.

We found that $4.50$ is the cost when $m = 0$, meaning the customer pays $4.50$ even if the taxi does not travel any miles. That is exactly the flat starting charge for using the taxi.

So, $4.50$ represents the flat fee charged before any miles are driven.