Answer:
Please see attached picture for full solution.
D=4(9-c) and d=2(9+c)
d=36-4c and d=18+2c
Since d=d
18+2c=36-4c add 4c to both sides
18+6c=36 subtract 18 from both sides
6c=18 divide both sides by 6
c=3
So the speed of the current is 3mph
The answer is 8:14. this can be simplified to 4:7 (divide by 2).