it is math 307 about the differential equation

9. + -/3 points My Notes A spherical 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. The volume of the drop: dt The radius of the drop: dt The surface area of the drop: ds dt