Applying GP test

The numbers \(q\), \(q+5\), \(q+15\) are the \(3^{\mathrm{rd}}\), \(4^{\mathrm{th}}\) and \(5^{\mathrm{th}}\) terms of a geometric progression. Find the value of \(q\) and the \(8^{\mathrm{th}}\) term.