SELECT "R 51 O" FROM table_78137 WHERE "D 42 O" = 'r 19'
Which R 51 O value corresponds to a D 42 O value of r 19?
CREATE TABLE table_78137 (
    "D 41 O" text,
    "D 42 O" text,
    "D 43 O" text,
    "D 44 O" text,
    "D 45 +" text,
    "R 55 +" text,
    "R 54 +" text,
    "R 53 +" text,
    "R 52 O" text,
    "R 51 O" text
)