Answer:

k = 3.022
Step-by-step explanation:
Given that:
A spherical raindrop evaporates at a rate proportional to its surface area.
The surface area SA of a spherical object is given by the relation:
SA = 4πr²
Write down a differ- ential equation for its volume as a function as a function of time.
So; to differentiate Volume (V) in respect to time (t) ;then:

Likewise; we know known that the volume of a sphere V = 
Thus, from above;




Thus; solving the differential:


So;
we are to find the constant proportionality K
If Volume V = 1 cm³ and the time = 10 sec

0.1 = - 4π k (0.3848 × 1)
0.1 = - 4π k × 0.3848
4π k = 0.3848/0.1
4π k = 3.848
k = 3.848/4π
k = 3.022