7. (5 points) As shown in the figure, there is a cross-shaped shaded area formed by two rectangles in the middle of a rectangle that is 9 cm long and 8 cm wide. If the area of the shaded part is exactly equal to the area of the blank part, then $X=$ $\qquad$ cm.


【Analysis】According to the figure, the area of the shaded part is 3 times 8 plus 9 times $x$ minus the overlapping part $3 x$, and the area of the blank part is 9 minus 3 times the difference of 8 minus $x$. Since the area of the shaded part is equal to the area of the blank part, each occupying half of the total area, we can set up an equation to solve it.

【Solution】Solve: $3 \times 8+9 x-3 x=9 \times 8 \times 0.5$,
$$
\begin{aligned}
24+6 x & =36, \\
6 x & =36-24, \\
x & =2,
\end{aligned}
$$

Therefore, the answer is: 2.