Hi there!
Recall the equation for electric potential of a point charge:

V = Electric potential (V)
k = Coulomb's Constant(Nm²/C²)
Q = Charge (C)
r = distance (m)
We can begin by solving for the given electric potentials. Remember, charge must be accounted for. Electric potential is also a SCALAR quantity.
Upper right charge's potential:

Lower left charge's potential:

Add the two, and subtract from the total EP at the point:

The remaining charge must have a potential of 2036.25 V, so:

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