Question 1101434
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Let D be the unknown distance under the question, in kilometers.


Then the time spent traveling at the speed 12 km/h is {{{D/12}}} hours.

     The time spent traveling at the speed  9 km/h is {{{D/9}}} hours.

The total time equation is 

{{{D/12}}} + {{{D/9}}} = {{{3}}}{{{1/2}}}   hours,   or

{{{D/12}}} + {{{D/9}}} = {{{7/2}}}.


Multiply by 36 both sides.  You will get

3D + 4D = 7*18,   or

7D = 7*18  ====>  D = 18 kilometers.


<U>Answer</Y>. The one way distance is 18 km.
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