Question 1137486
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Obviously, Colin is the eldest.


Let C be the Colin's age.


Then we have an equation


(C-9) + C + ((C-9)-12) = 93


3C - 30 = 93

3C = 93 + 30 = 123

C = 123/3 = 41.


<U>ANSWER</U>.  The eldest, Colin, is 41 years old.


<U>CHECK</U>.  Then Richard is 41-9 = 32 years old;  David is  32 - 12 = 20 years old  and

        41 + 32 + 20 = 93.   ! Correct !
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Solved.