First charge q1= 20 x 10-6
Second charge q2= 80 x 10-6
Distance d =10cm
Let the electric field will be zero at point O.
Two point charges 20 micro coulomb and 80 micro coulomb are 10 cm apart at point A and B.
The distance between O and A is (10-x) cm and the distance between O and B is x cm.
Hence, The electric field will be zero at 6.67 cm distance from 80 micro coulomb.