Question 1117747
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The equivalent re-formulation is THIS:



    Mike charged x;  Tony charged 3x;  Dave charged 12x.



Then in all, they charged x + 3x + 12x = 16x,  which is  sh480;  hence,  x = {{{480/16}}} = 30.


Thus Mike charged  sh 30;  Tony charged  sh 90;  and Dave charged  sh 360.


You can do the rest.
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