A motorboat travels

Question

A motorboat travels 423 kilometers in 9 hours going upstream and 651kilometers in 7 hours going downstream. What is the rate of the boat in still water and what is the rate of the current?

Answer 1

d=rt

t=d/r

423 = (b-c)9

651 = (b+c)/7

423/9 = 47 = b-c

651/7 = 93 = b+c

add 140 = 2b

b = 70 km/h for the motorboat in still water

c =b-47 = 23 km/h for the current rate