4. (8 points) $A$, $B$, and $C$ are picking watermelons.
The sum of the number of watermelons picked by $A$ and $B$ is 6 less than that picked by $C$;
The sum of the number of watermelons picked by $B$ and $C$ is 16 more than that picked by $A$;
The sum of the number of watermelons picked by $C$ and $A$ is 8 more than that picked by $B$;
How many watermelons did they pick in total? $\qquad$
【Solution】Solution: According to the analysis, the first sentence gives us, $C-(A+B)=6$; the second sentence gives us, $B+C-A=16$; the third sentence gives us, $C+A-B=8$; adding the three equations together, we get:
$$
\begin{array}{l}
(A+B-C)+(B+C-A)+(C+A-B)=-6+16+8 \\
\Rightarrow 2(A+B+C)-(A+B+C)=A+B+C=18
\end{array}
$$
$\therefore$ They collected a total of 18 watermelons.
Therefore, the answer is: 18.