30. The following is a map of the administrative districts of Jintan City. Now, we are to color the four uncolored districts of the city using brown, green, yellow, and pink. If it is required that adjacent (sharing a common border) districts have different colors, how many coloring methods are there in total?



The text has been translated while preserving the original formatting and line breaks.
30. The following is a map of the administrative districts of Jintan City. Now, we are to color the four uncolored districts of the city using brown, green, yellow, and pink. If it is required that adjacent (having a common boundary) districts have different colors, how many coloring methods are there in total?
【Analysis】According to the problem, we will discuss the cases separately: (1) Zhixi Town and Zhiqian Town are the same color. (2) Zhixi Town and Zhiqian Town are different colors. By the principle of addition for classification, the answer can be calculated.

【Solution】Solution: We divide it into two cases:
(1) Zhixi Town and Zhiqian Town are the same color

Coloring Zhixi Town and Zhiqian Town: 3 cases; Coloring Zhulin Town: 2 cases; Coloring Xuebu Town: 2 cases, totaling $3 \times 2 \times 2=12$ cases;
(2) Zhixi Town and Zhiqian Town are different colors

Coloring Zhixi Town and Zhiqian Town: 6 cases; Coloring Zhulin Town: 1 case; Coloring Xuebu Town: 1 case, totaling $6 \times 1 \times 1=6$ cases;

In summary, there are $12+6=18$ coloring methods.