[填空题]
The first term and thrc x)z(9lpd(ve common ratio of a geometric series are denoted, rxgoe1 k )u*nt(espectively, bxt*ne k)o1g u(y $u_{1}$ and r , where $u_{1}$, $r \in \mathbb{Q}$ . Given that the fourth term is 64 and the sum to infinity is 625 , find the value of $u_{1}$ and the value of r .$u_{1}$ = r =
