For Exercise, refer to Figure A, which follows. At the beginning of this section it was me...

For Exercise, refer to Figure A, which follows. At the beginning of this section it was mentioned that for sufficiently short periods of time, the graphs of many real-world quantities can be approximated quite accurately by a straight line. For instance, the following graph provides a close approximation to U.S. population data for the years 1970–1990.

Figure A

U.S. population (as of July 1) for years 1970–1990

Adapted from U.S. Bureau of the Census data

What is the slope of the population graph in Figure A? (Be sure to include units with your answer.)