{This game] I think must be won for white. But you should not play Rxc4 as after bxc4, white will immediately play c5, trade pawns and pick off the a pawn.
White really needs the N. If you play another move Nxb4, axb4 etc you must make it difficult for the B and try to run your 4pawns. He must play Be6,then Kf6. It is still lost but a timely e4 fxe4 Ke5 may cause problems. The white K has to go to collect the b4 and b6 pawns. But still lost if white knows what he is doing. The white squares are key
Some analysis from Geoff Frost:
{This game] I think must be won for white. But you should not play Rxc4 as after bxc4, white will immediately play c5, trade pawns and pick off the a pawn.
White really needs the N. If you play another move Nxb4, axb4 etc you must make it difficult for the B and try to run your 4pawns. He must play Be6,then Kf6. It is still lost but a timely e4 fxe4 Ke5 may cause problems. The white K has to go to collect the b4 and b6 pawns. But still lost if white knows what he is doing. The white squares are key