Finding the Constant of Proportionality from a Graph A graph titled Swimming Pool has time (hours) on the x-axis and Depth of Water (feet) on the y-axis. At 1 hour the depth is 1.5; 2 hours, 3 feet; 3 hours, 4 feet; 4 hours, 6 feet. Pauly is filling his swimming pool with water at a constant rate. The graph shows the amount of water added over time. What is the unit rate? 1 foot per hour 1.5 feet per hour 2.5 feet per hour 3 feet per hour