For the logarithmic inequality in $x$
$$\log _ { 5 } ( x - 1 ) \leq \log _ { 5 } \left( \frac { 1 } { 2 } x + k \right)$$
when the number of all integers $x$ satisfying this inequality is 3, what is the value of the natural number $k$? [3 points]\\
(1) 1\\
(2) 2\\
(3) 3\\
(4) 4\\
(5) 5