Hint: whoever made up this scenario is either sadist or is trying to make a point that Airbus doesn't include everything that it should in manuals (I have to concur on that).
Factor 2.45 for landing with blue hyd only, caters for loss of normal braking, alternate braking, most of the ground spoilers and flaps. However in your case, with flaps locked at 3, your Vapp should be Vref+10, not Vref+25 as in the case of G+Y HYD loss. So you have to take the factor for Flaps=3 and slats=3 (1.25) and multiply it with factor for accu braking only on contamined runway.
Oh, bugger, it seems that neither of these is included in FCOM.
Now, if my assumptions are correct, to get factor of 2.45, Airbus has multiplied factors for increased Vref and loss of normal braking. Factor for landing with flaps and slats stuck at three is 1.25 and for slats 3 and flaps zero is 1.60 on contamined runway. If ve divide 2.45 with 1.6, we get 1.53, which is (I think... I guess.. I hope) our accu braking only factor. Now we'll multiply it with 1.25, for conf3 landing and our coveted factor turns out to be 1.913.
However, if there's another clean runway nearby, I wouldn't be courageous enough to check whether my calculations are correct. And with gear stuck down, you'd be lucky to get 70 miles out of a ton of fuel. And with flaps hanging out too, it would be even less.
So it easily turns into the case of landing notwithstanding legality and trying to overrun with the least possible speed. Good thing it's sim scenario only.