I need help solving a word problem

Question

A motorboat goes 5 miles upstream in the same time it requries to go 7 miles downstream, If the river flows 2 miles per hour, find the speed of the boat in still water.

Answer 1

Speed = distance/time

s = d/t

t = d/s

b is the speed of the boat in still water, and c is the speed of the river.

c = 2 mph

Down stream speed = b + c 

Up stream speed = b - c

Time up stream = Time down stream

Distance upstream/Speed upstream = Distance down stream/Speed down stream

Down stream distance = 7

Upstream distance = 5

The rational equation is 5/(b - 2 ) = 7/(b + 2)

5 (b + 2) = 7(b - 2)

5b + 10 = 7b - 14

5b - 7b = - 14 - 10

- 2b = - 24

b =  24/2

b = 12

Speed of the boat in still water 12mph.

Comments

Should it be 5(2+c)=7(2-c)

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Since the variable c represents the speed of stream is 5 (b + 2) = 7(b - 2) and not 

5(2 + c)=7(2 - c), where b is speed of boat .