Question 1059463
The sum of the ages of Mark's two sons is equal to his own age of 51. 
21 years ago, Mark's older son was twice as old as the younger son. 
How old was Mark when the sum of his sons' ages was half his age?
<pre>Mark was: {{{highlight_green(matrix(1,2, 34, years-old))}}} when he was twice the sum of his sons' ages.
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