Respuesta :

Answer:

7 or 8 miles per hour

Step-by-step explanation:

Answer:

2.1429 or 2 and 1/7

Step-by-step explanation:

Time = time

12/(15+c)=9/(15-c)

12(15-c)=9(15+c)

12*15-12c =9*15+9c

21c=3*15

c=3*15/21

c=45/21=2.1429..(speed of the current)

Downstream info;

distance=12miles;rate=15+c mph; time=d/r =12/(15+c)hrs.

Upstream info;

distance=9miles;rate=15-c mph;time=d/r=9/(15-c)hrs.

I hope it's helpful!