Step-by-step explanation:
Formula to calculate the electric potential is as follows.

Putting the given values into the above formula as follows.

=
![(9 * 10^(9))/(0.25)[(-3.3)/(√(2)) + 4.2] * 10^(-6)](https://img.qammunity.org/2021/formulas/physics/high-school/1u1s4dei1m3qvfpv54rwl3cbdq1eg60jk7.png)
=

Hence, electric potential at point A is
.
Now, the electric potential at point B is as follows.

=
![(9 * 10^(9))/(0.25) [-3.3 + (4.2)/(√(2))] * 10^(-6)](https://img.qammunity.org/2021/formulas/physics/high-school/e8lz6euquvy50jjh7tgu1eml89oh6v1usj.png)
=

Hence, electric potential at point B is
.