A linear model with a flat fee plus a per-mile rate gives each number a different job: one is charged once, and the other grows with the miles driven. To interpret the number standing alone, evaluate the cost at zero miles; Desmos can check that starting cost. Watch for a mileage charge that happens to equal the flat fee numerically but comes from a different part of the equation.
Hints
- Hint 1
The input is the value you put into a rule. Here, miles are the input, so before any miles are driven means what value of ?
- Hint 2
The term grows with the miles driven, while a flat fee is charged once. At zero miles, which part of the cost remains?
Step-by-step
Check the cost at zero miles
Step 1Identify the starting input
The starting value is the cost when the input is zero. Since counts miles, before any miles are driven means . Set the input to zero to identify the fixed charge.
- Step 2
Evaluate and interpret the starting cost
Type in Desmos, using as the name for the given cost rule. Then type . Desmos displays , so the cost at zero miles is $4.50. That makes the flat fee charged before any miles are driven. Choice B.