10.6 An apple slice with 1 cm thickness is exposed to 80% RH for one week. After one week, the water activity of the apple has increased to 0.6, from an initial value of 0.1. The convective mass transfer coefficient at the product surface is 0,008 m/s. Estimate the mass diffusivity for water vapor in the apple.

the question from "introduction to food engineering" (Book)