By Stefan 's law  -(dQ/dt)=Ae*(stefan const)*T^4

dQ=ms(dT)

from 2 eqns get

-(dT/dt)=(Ae*(stefan const)*T^4)/(ms)

m=(4/3*pi*r^3)*(density)

substitute the values in the eqn and get (R2*d2*c2)/(R1*d1*c1)