A service attendant accidently spills 50 litres of gasoline, which quickly spreads over a level surface of area 8 m 2. Estimate the time required for the gasoline to evaporate into the stagnant air...

A service attendant accidently spills 50 litres of gasoline, which quickly spreads over a level surface of area 8 m^2.
Estimate the time required for the gasoline to evaporate into the stagnant air above the surface of the liquid. The diffusivity of gasoline in air is 0.65 m²h^-1
.The air temperature is 298 K. Evaporation may be assumed to take place through a film of air of 2 m thickness. Vapour pressure of gasoline at 298 K is 76 mm Hg. The density of gasoline is 720 kg m^-3
and the molecular weight of gasoline is 200. The operation takes place at 1 atm pressure.