With the defending king on the edge opposite the attacking king and the rook unable to reach the long side, White wins by a known manoeuvre: check, rook to the seventh, drive the rook to the first rank, interpose the bishop, and mate or win the rook.
Rook and bishop against rook is a draw in general, but Philidor showed a position where it is won, and most practical wins pass through it. Black's king is on d8 opposite the white king on d6, the bishop on d5 covers the long diagonals, and the black rook on e2 has been pushed to the second rank.