How Does a Dual Ring Charge Configuration Affect Electric Potential?

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Homework Statement

what is the electric potential a distance x above the center of a ring of charge Q with a radius R surrounded by another ring of charge -Q with a radius 2R?

Homework Equations

V= kQ/sqr root(a^2+x^2)

The Attempt at a Solution

I know the above equation would be used for for one ring but would the second ring in this problem effect this equation?

 

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anyone? I could really use some help on this one and thanks in advance to anyone who can help!