r is the distance between the center of the Earth and the object in question. That is the symbol people usually use but I just noticed the picture you showed uses "d" to represent that distance so r is the same as your d.
Ok please bear with me if I sound dumb...never taken physics before so I'm finding it realli difficult
So do I have to find m1 and m2? And for G I've been given an approximation for it, and I dunno if I'm suppose to use it