For a $22$-mile trip, what is the expression for the mileage cost using $0.40$ dollars per mile? Plug this into an equation where total cost equals booking fee plus mileage cost.

Once you have an equation like $b + \text{(mileage cost)} = 15.80$, what operation should you use to get $b$ by itself?

In a new expression line, type 15.8 - 0.40*22 to represent total cost minus mileage cost. The numerical result that Desmos displays is the booking fee for the trip.

The total cost of the trip equals the fixed booking fee plus the cost per mile.

Let the booking fee be $b$ dollars.

For a $22$-mile trip, the cost per mile is $0.40$ dollars, so the mileage cost is $0.40 \times 22$.

So the equation for the total cost is:

Calculate the cost for the $22$ miles:

Now substitute that back into the equation:

To solve for $b$, subtract the mileage cost $8.8$ from both sides of the equation:

This simplifies to:

Now do the subtraction:

So the booking fee is $b = 7$ dollars, which is $7.00$.

The correct answer is $7.00$ (Choice C).