1. The problem statement, all variables and given/known data Assuming that the rate of the mass (m) of an object is proportional to its total surface area, derive a D.E for the rate of change in the mass. Arbitrary constants may be included. The objects in question are expanding peat discs. The discs absorb water through their surface which causes an increase in height (but the radius and density remain constant). 2. Relevant equations None 3. The attempt at a solution No idea... Not even sure where to start? dm/dt = ...?