The underground storage of a gas station has leaked gasoline into the ground. Among the constituents of gasoline are benzene, with a Kd value of 1.8 L/kg for the soil in that location, and toluene, with a Kd of 3.3 L/kg. The soil has a solids density of 2.6 kg/L and a hydraulic conductivity of 2.9 × 10^-5 m/s and is 37% pores (by volume). The site is to be remediated by pumping out and treating groundwater from a well 15 m downgradient from the site of the spill, where the water table is 0.4 m lower than at the leaking tank. How long will it take for:

a. benzene
b. toluene to reach the well?