35. Lusi Xi recently fell in love with paper folding. She found that if the paper is folded as shown in the figure, with line $E F$ as the crease, point $D$ is folded to $D^{\prime}$, $E D^{\prime} / / A B$, and $D^{\prime} F / / B C$. When the area of the shaded part is equal to the area of the blank part, the length of the crease $E F$ can be calculated if the area of the paper is known. If the area of Lusi Xi's square paper $A B C D$ is 108 square centimeters, the length of the crease $E F$ is $\qquad$ centimeters.
$12$