MC react to distance

I’ve had a long look and simply couldn’t find any help for what it is I’m trying to do.

I want it so that when a movie clip is dragged to a new location, the distance from the MC and another MC is calculated. And when the distance has reached a certain amount (200+ pixels for example) it will react (go to a new frame).

I’ve attached a partial, any help or guidance would be really appreciated.

Thanks