Respuesta :

hanhtetsan

Answer:

7 hours

Step-by-step explanation:

just multiply 3 and 7 to get 21

Answer:

[tex]\fbox {7 hours}[/tex]

Step-by-step explanation:

⇒ Rate = -3F/hour

⇒ Starting : -21F

Solving :

⇒ -21/-3

⇒ 7 hours