Answer:
The speed of the boat in still water is 15mile/hour
Explanation:
Upstream data:
Distance=11mile , rate = b - 4mph
Time=distance/rate = 11/(b-4)
Downstream data:
Distance =19miles , rate = b + 4mph
Time= distance/rate= 19/(b + 4)
Time upstream = time downstream
11/(b-4) = 19/(b+4)
Cross multiply
11(b+4) = 19 (b-4)
11b + 44 = 19b - 76
Collecting like terms
19b - 11b = 76 +44
8b= 120
b= 120/8 = 15mile/hour
