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