18. (6 points) Given the four-digit number $\overline{\mathrm{ABCD}}$, the conclusions of three people, Jia, Yi, and Bing, are as follows:

Jia: “The unit digit is half of the hundred digit”;
Yi: “The tens digit is 1.5 times the hundred digit”;
Bing: “The average of the four digits is 4”.
According to the above information, we can get: $\overline{\mathrm{ABCD}}=$
【Solution】Solution: According to the analysis, from A's statement, we know that the digit in the hundreds place must be even.
From the statements of the three people, we can derive the equation, $A+B+C+D=4 \times 4 \Rightarrow A+2 \times D+2 \times 1.5 \times D+D=16$ $\Rightarrow A=16-6D ; \quad \because 1 \leqslant A \leqslant 9, \quad \therefore 1 \leqslant 16-6D \leqslant 9 \Rightarrow \frac{7}{6} \leqslant D \leqslant \frac{5}{2}$,

Also, $\because D$ is a non-negative integer, $\therefore D=2, A=16-6 \times 2=4$;
In summary, $B=2 \times 2=4, C=1.5 \times 4=6, \overline{\mathrm{ABCD}}=4462$
Therefore, the answer is: 4462.