Need to identify hinge part for Pella Casement window - need to know if it RH or LH hinge

The left and right hinge is determined from the exterior of the window, not the interior. I am afraid though that your best bet is to remove yours from the window and compare it to our pictures. There's just too much variation based on the exact setup of the window otherwise. At any rate, you'll need to remove the hinge anyways to get the exact dimensions. See the list I've placed on this page.