Translate the problem into a pair of linear equations in two

Translate the problem into a pair of linear equations in two vaiables. Solve the equations using either elimination or substitution. State your answer for the specified variable.
The speed of a current is 6 mph. If a boat travels 62 miles downstream in the same time that it takes to travel 31 miles upstream, what is the speed of the boat in still water?

Solution

Downstream DATA:
distance = 62 miles ; rate = b+6 ; time = 62/(b+6) hrs
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Upstream DATA:
distance = 31 miles ; rate = b-6 ; time = 31/(b-6) hrs
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Equation:
time down = time up
62/(b+6) = 31/(b-6)
Cross-multiply to get:
62(b-6) = 31(b+6)
62b - 6*62 = 31b + 31*6
31b = (31+62)6
b = 18 mph (speed of the boat in still water)
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