Hi, sorry if this is too late. Is it possibly a typo, and d>>r0, in which case you can treat the spheres as point charges when considering the field between them. If they are collided, ie as the question says d<<r0, then treat it was one sphere I suppose. Using gauss' law the field outside the spheres (which will appear as a single sphere as their centres are practically the same) will be zero as there will be zero net enclosed charge.