7. A plumbing company installs tankless hot water heaters and charges for both installation time and materials used. a. The heater and supplies cost \( \$ 1800 \) and the shop charges \( \$ 110 / h \)
for a plumber and an apprentice. Write an equation to represent the total cost to the customer. Be sure to state what each variable represents. b. i. What is the slope of the relation? c. Sketch the graph of the relation.