Question 1016118
The volume of a sphere is,
{{{V=(4/3)pi*R^3=(4/3)pi(D/2)^3=(pi/6)D^3}}}
So the total volume of the new sphere is,
{{{V[n]=(pi/6)(2^3+12^3+16^3)=(4/3)pi*R^3}}}
{{{R^3=(2^3+12^3+16^3)/8}}}
Take the cube root,
{{{R=((2^3+12^3+16^3)/8)^(1/3)}}}