Berapa kah hasil dari 21per28-6per14:9per25

Berapa kah hasil dari 21per28-6per14:9per25

$frac{21}{28} - frac{6}{14} div frac{9}{25} \ = frac{21}{28} - ( frac{6}{14} times frac{25}{9} ) \ = frac{21}{28} - ( frac{2}{14} times frac{25}{3} ) \ = frac{21}{28} - frac{50}{42} \ = frac{126 - 200}{168} \ = frac{ - 74}{168} \ = frac{ - 37}{84}$