Answer:
Step-by-step explanation:
b = speed of boat in still water
traveling downstream, the boat goes (b+4 miles)/hour.
traveling upstream the boat goes (b-4 miles)/hour.
Time to travel 17 miles downstream = 17 miles × (1 hour)/(b+4 miles)
Time to travel 9 miles upstream = 9 miles × (1 hour)/(b-4 miles)
17 miles × (1 hour)/(b+4 miles) = 9 miles × (1 hour)/(b-4 miles)
17/(b+4) = 9/(b-4)
cross-multiply denominators:
17(b-4) = 9(b+4)
17b - 68 = 9b + 36
8b = 104
b = 13 miles per hour
