Una plataforma de 30 pies de largo y seis pies de ancho (also de 30 pies por seis): A platform 30 feet long by six feet wide.
Este tanque tiene 16 pies de profundidad: This tank is 16 feet deep.
"In" after a superlative relative is rendered by de, as—
Es el negociante más próspero de la ciudad: He is the most successful merchant in the city.
The proportional adjectives are—
El doble (the double)
El triple (3 fold)
El cuádruplo (4 fold)
El quíntuple (5 fold)
El séxtuple (6 fold)
El décuplo (10 fold)
El céntuplo (100 fold)
Siete veces tanto (7 fold)
Ocho veces tanto (8 fold). Etc., etc.
The adjective is used also adverbially, oftener in Spanish than in
English, as—
Hablar claro, alto, bajo, fuerte: To speak clearly, loudly, softly, strongly.
Comprar caro, barato: To buy dear, cheap.
Ir derecho: To go straight.