Aspherical raindrop evaporates at a rate proportional to its surface area with (positive) constant of proportionality k ; i. e. the rate of change of the volume exactly equals −k times the surface area. write differential equations for each of the quantities below as a function of time. for each case the right hand side should be a function of the dependent variable and the constant k . for example, the answer to the first question should not depend on s or r .