A spherical droplet of liquid A and radius ro evaporates into a stagnant layer of gas B. Derive an expression for the evaporation rate of species A in terms of the saturation pressure of species A, pA(ro) = PA,sat, the partial pressure of species A at an arbitrary radius r, pA(r), the total pressure p, and other pertinent quantities. Assume the droplet and the mixture is at a uniform pressure P and temperature T.