A linear model fits a fixed fee plus a charge that repeats for each item. Write the total as the fixed fee plus the per-item price times the number of items, then evaluate that rule in Desmos. The fixed fee stays outside the multiplication; multiplying it by the item count charges it repeatedly.
Hints
- Hint 1
A flat fee is charged once for the month, even if no movies are rented. Which price should stay unchanged when you write the total charge?
- Hint 2
A per-movie rate repeats with every rental. Multiply that rate by the number of movies, then add the monthly fee once. What movie count will you use to find March’s charge?
Step-by-step
Build and evaluate the charge rule
Step 1Write the total charge
Let be the number of movies rented, and let be the total charge in dollars. The $8 flat fee is paid once, while the $2 per-movie rate is paid times. So multiply only the per-movie charge by the movie count:
- Step 2
Find Lena’s March charge
Type in Desmos, then type . This puts Lena’s 5 movies into the function, or charge rule. Desmos displays , so her total charge for March was $18. Choice B.