The Rook - horizontal moves 2
The rook on a12 can traverse the entire width of the board unimpeded. All the fields are empty apart from the black pawn on e14. The rook cannot take the black pawn but it could occupy any of the squares b12-h12, a11-d11 and f11-h11.
The rook on a8 is blocked by a black pawn on e8. The rook can occupy any of the squares in empty fields b7/8-d7/8 or a7. It can also capture the black pawn on e8.