Question 152546
Let Chan be C years old.
His cousin, Zeke (we'll call him that), is Z years old.
"Chan is 4 times older than Zeke."
1.{{{C=4Z}}}
In 8 years, Chan will be (C+8) years old and Zeke will be (Z+8) years old. 
"In 8 years Chan will be two times older than Zeke."
2.{{{(C+8)=2(Z+8)}}}
2.{{{C+8=2Z+16}}}
Substitute eq. 1 into 2 and solve for Z.
2.{{{C+8=2Z+16}}}
{{{4Z+8=2Z+16}}}
{{{2Z=8}}}
{{{Z=4}}}
Then from eq. 1,
1.{{{C=4Z}}}
{{{C=4(4)}}}
{{{C=16}}}
Check the answer.
In eight years, Chan will be 24 and Zeke will be 12.