ANSWER
Earl =12 years, Robin =24 years and Adam =4 years.
EXPLANATION
Let Earl's present age be
[tex]e \: \: years[/tex]
Then Robin will be,
[tex]2e \: \: years[/tex]
and Adam will be
[tex](e - 8) \: \: years[/tex]
In six years time, Robin will be 3 times as old as Adam. This implies that,
[tex]2e + 6= 3(e - 8 + 6)[/tex]
[tex]2e + 6= 3(e - 2)[/tex]
We expand to get,
[tex]2e + 6= 3e - 6[/tex]
Group similar terms to get;
[tex]3e - 2e = 6 + 6[/tex]
This implies that,
[tex]e = 12[/tex]
Therefore their present ages are;
Earl =12 years, Robin =24 years and Adam =4 years.