How to find overlapping distance between 2 entities

I need to find the distance one entity overlaps another so I can move the first away from the second by that amount. I remember seeing things to do this, I just can;t seem to find the posts/tutorials.
I’ve tried something like partA.getposition() - partB.getposition(); but this doesn’t seem to work.

function distanceBetween(entityA, entityB) {
    var posA = entityA.getPosition();
    var posB = entityB.getPosition();

    var dx = posB.x - posA.x;
    var dy = posB.y - posA.y;
    var dz = posB.z - posA.z;

    return Math.sqrt(dx * dx + dy * dy + dz * dz);

var dist = distanceBetween(entityA, entityB);

Right, I thought there was more to do than I had, thanks!

EDIT: I just realized this will move the object linearly out of the other by the shortest route. Is there a way to make it angular so I can rotate the object away from the other on one axis? (should have mentioned this in my first post, sorry)

Here’s a link to my project to help get an idea of what I’m trying: