Question 1116802
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Let L be the one way distance.


Then you have this "time" equation to find L:

{{{L/8}}} + {{{L/24}}} = {{{3/4}}}   of an hour.      (!)


It is "time" equation, because each fraction in the left side is the time to cover the distance L at the corresponding speed.


From equation (1), after multiplying its both sides by 24, you have


3L + L = 3*6,   or

4L = 18  ====>  L = {{{18/4}}} = {{{9/2}}} = {{{4}}}{{{1/2}}} = 4.5 km.


<U>Check</U>.  {{{((9/2))/8}}} + {{{((9/2))/24}}} = {{{9/16}}} + {{{9/48}}} = {{{27/48}}} + {{{9/48}}} = {{{36/48}}} = {{{3/4}}} of an hour.   ! Correct !
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Solved.