Question 29959
Let the speed of the boat in still water be x
Against = -
"back again" = +
5hours and 20 minutes  =5 1/3--->16/3


Equation;
 {{{12(x-3)=(16(x+3))/3}}}
Expand:
{{{12x-36=(16x+48)/3}}}
Multiply the whole equation by 3 to remove the fraction:
{{{3((12x-36)/1)=3((16x+48)/3)}}}
*[tex 3(12x-36)=16x+48]

*[tex 36x-108=16x+48]

*[tex 20x=156]

*[tex x=7.8]


<font color = dark blue>Hence, the speed of the boat is 7.8mph in the still water.</font>
Paul.