9. (8 points) A resident is renovating their house and has bought several pieces of wooden strips, some 0.7 meters long and others 0.8 meters long. If some of these strips are joined together, many different lengths can be obtained, for example, $0.7+0.7=1.4$ (meters), $0.7+0.8=1.5$ (meters), etc. Therefore, the length of the wooden strip in the box below, $\qquad$ meters, cannot be obtained by joining these strips.
【Answer】Solution: $3.6=0.7+0.7+0.7+0.7+0.8$;
$$
\begin{array}{l}
3.7=0.7+0.7+0.7+0.8+0.8 ; \\
3.9=0.7+0.8+0.8+0.8+0.8 ; \\
3.8=0.7+0.7+0.8+0.8+0.8 ;
\end{array}
$$

Only 3.4 is not possible.