Answer:
¿Qué hora es? (6:45): Son las siete menos cuarto.
Explanation:
Cuarto is to represent 15 minutes, so "Son las siete menos cuarto" means it's 7 o' clock minus 15 minutes. For anything past the half hour (30), instead of seis {minutes}, it'll be siete menos {minutes}. That's what I learned in my Spanish last year at least.
