1. The problem statement, all variables and given/known data A spherical mothball of original radius 1.2 cm slowly evaporates such that 180 days later, its radius is only 1 cm. Physically, the rate of evaporation dr/dt is proportional to the surface area of the sphere. Determine a) the time required for the radius of a new mothball to shrink to 25 percent of its original radius, and b) the time required for the volume of a new mothball to become half of its original value. 2. Relevant equations SA= 4 pi r^2 r(0)=1.2 r(180)=1 3. The attempt at a solution I started by saying -dr/dt = c1 4 pi r^2 where c1 is a constant of proportionality Then through separation of variables I found that 1/r = 4 pi c1 t + c2 after imposing the initial conditions I found c1=7.383*10^-5 and c2=.833 so I have 1/r = 4 pi (7.383*10^-5) t + .833 and this gives me answers of 1) 2694 yr 2) 233.82 yr but these aren't right. Any ideas of where I went wrong?