Question 829538
Let {{{A}}} be Jill's age.
Let {{{B}}} be Jack's age.
1.{{{A=B+12}}}
In 8 years, Jill will be A+8, I assume you mean 3 times his age right now (because otherwise it doesn't work)
2.{{{A+8=3B}}}
Substitute eq. 1 into eq. 2,
{{{B+12+8=3B+24}}}
{{{B+20=3B}}}
{{{2B=20}}}
{{{B=10}}}
From eq. 1,
{{{A=10+12}}}
{{{A=22}}}
Jack is 10 and Jill is 22 years old.