3. If $\triangle A B C$ has exactly one solution when $\angle A B C=60^{\circ}, A C=12, B C=$ $k$, then the range of values for $k$ is $\qquad$
$3.0<k \leqslant 12$ or $k=8 \sqrt{3}$. As shown in Figure 4, we can obtain
$$
0<k \leqslant 12
$$

or $k=8 \sqrt{3}$.