Question 1201539
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Let x be the speed of the boat in still water in km/hr. Then a single equation to set up the problem says that the distance covered in 12 hours at a speed of (x-4) km/hr is 30 km more than the distance covered in 8 hours at a speed of (x+4) km/hr:<br>
{{{12(x-4)=8(x+4)+30}}}
{{{12x-48=8x+62}}}
{{{4x=110}}}
{{{x=27.5}}}<br>
The boat speed in still water is 27.5 km/hr<br>
The distance D is the distance covered in 8 hours at a rate of (x+4) km/hr: D = 8(31.5) = 252<br>
The time required to cover a distance of D-64 = 188 km at a rate of (x-4) = 23.5km/hr is<br>
{{{188/23.5=376/47=8}}}<br>
ANSWER: 8 hours<br>