Hi Candidate,

The the ter minal velocity formula , v = the square root of ((2*m*g)/(ρ*A*C)). Here are two spheres of radii r and 2r, so the new spherical radius is-

R.R.R = r.r.r + 2r.2r.2r = 9r.r.r, So the value of R equals cube root of 9. Hence, the terminal velocity equals to ((2*m*g)/f*A*C), where f refers to density and A refers to 4*22/7*R.R.

Hope that you have got your answer. All The Best.

Have a Good Day. Thank You!!