Potential difference Calculation

[Tan_Can]

I am stuck on this question about potential difference, the question is: each side of an equilateral triangle measures 3.61cm. A charge of -0.34mC is placed at each vertex. what is the potential difference at the midpoint of the base of the triangle, i need quick help. Thank you.

 

[basePARTICLE]

Sum the potentials arising from the charges, after drawing the vector diagram.