At distances of 5 cm and 10 cm from the surface of a sphere, the potentials are 600 V and 420 V. Find the potential at its surface

potential at distance 5cm from the surface kqr+0.05=600 V  ---1 potential at a distance 10 cm from the surface  kqr+0.1= 420 V ----2 dividing we get r= 0.2/3 potential at the surface kqr=v ----3         dividing 1 by 3 we get v=1050 V