let the mid point of base is p..

distance of q charge from P is (4² -1²)^1/2 =sqrt15cm....           (by using pythogorus theorem)

                                                             =sqrt15x10^-2m

potential due to q charge is V_q= kq/r

                                           = 100kq/sqrt15 ...........1

distance of any -q charge from p is 1cm

potential due to two -q charges at p will be

           2V-q = -2x100kq

                  =-200kq     .........2

net potential is addition of these

        V_T =  -200kq + 100kq/sqrt15

            =1.09x10⁷ V

            =

Approved