Answer:

Explanation:
We have given the radius of first sphere is 10 cm and radius of second sphere is 20 cm
So the potential of first sphere will be greater than the potential of the second sphere, so charge will flow from first sphere to second sphere
Let q charge is flow from first sphere to second sphere and then potential become same
So 
200-100=2q+q

So 
We know that potential energy U=qV