In a solar water heater, energy from the sun is gathered by water that circulates through tubes in a rooftop collector. The solar radiation enters the collector through a transparent cover and warms the water in the tubes; this water is pumped into a holding tank. Assume that the overall efficiency of the system is 20% (that is, 80% of the incident solar energy is lost from the system). What collector area is necessary to raise the temperature of 400 L (L = liters) of water in the tank from 20 C to 40 C in 1.0 hr when the intensity of incident sun light is 750 W/m^2? You need to know that the density of water is 1 kg/L.