The graph gives the number of gallons of water in a small swimming pool after x hours. Water (in gallons) 10000- 8000- 6000- 4000- 2000- 04 0 2 y=f(x) 4 6 Time (in hours) 8 (a) Write a formula for f(x). (b) Interpret both the slope and the y-intercept. (c) Use the graph to estimate how much water was in the pool after 7 hours. Verify your answer by valuating f(x).