Can anyone help me with a physics problem?

<p>I'm desprate, guys... i need help with two physics problems. Can anyone help? </p>

<p>The first one is this: </p>

<p>O
:
:
:
:________X</p>

<p>Okay at pointe O, the charge is 9 x 10^-6. At X, the charge is -1.1 x 10^-5. </p>

<p>O is 4 m away from the origin, and x is 7 m away. </p>

<p>The Coulomb constant is 8.98755 x 10^9.</p>

<p>I already found the magnitude of the resultant electric field at the origin (5443.23543). </p>

<p>Now I need to find the electric potential at the origin (V) and I just can't figure it out!</p>

<p>HELP!</p>

<p>wouldn't you do subtract the 2 charges? just a guess...but not sure...my physics teacher was horrible</p>

<p>I did find an equation...</p>

<p>it's UE = kQq/r</p>

<p>...hmmm</p>