1. The U.S. gross domestic product (GDP), y, for the years from 2011 and projected to 2021 is given by

t = 977.8x + 13,643.2

where x is the number of years past 1990 and y is in billions of dollars.

(a) What is the slope of the graph of this function?

(b) Interpret the slope as a rate of change.

2. An electric utility company determines the monthly bill for a residential customer by adding an energy charge of 8.38 cents per kilowatt-hour to its base charge of $16.37 per month. Write an equation for the monthly charge y in terms of x, the number of kilowatt-hours used?

3. Residential customers who heat their homes with natural gas have their monthly bills calculated by adding a base service charge of $9.19 per month and an energy charge of 91.91 cents per hundred cubic feet. Write an equation for the monthly charge y in terms of x, the number of hundreds of cubic feet used?