Let the common ratio of the first three numbers is \(r\) and the numbers be \(x_1,x_2,x_3,\) and \(x_4,\) respectively. Note that we can replace the value of the first number anytime with the fourth.
From the fact that the last three numbers are in an arithmetic sequence, we can rewrite the set as
\(x_2+12,x_2,x_2+6,x_2+12\)
We can then get the pair of equations
\(r(x_2+12)r=x_2\)
\(rx_2=x_2+6\)
Solving, we find that \(x_2=-4\) and \(r=-1/2\). Therefore, the set of four numbers is
\(\boxed{8,-4,2,8}\)
.