8. Square $A B C D$ has a side length of $10 \mathrm{~cm}$, point $E$ is on the extension of side $C B$, and $E B=10$ $\mathrm{cm}$, point $P$ moves on side $D C$, and the intersection of $E P$ and $A B$ is point $F$. Let $D P=x \mathrm{~cm}$, and the sum of the areas of $\triangle E F B$ and quadrilateral $A F P D$ is $y \mathrm{~cm}^{2}$. Then, the functional relationship between $y$ and $x$ is $\qquad$ $(0<x<10)$.
$\begin{array}{l}\text { S. } y=5 x+50) \text {. } \\ \text { H } I P=x \text { pending } P C=10 \quad x, J B=\frac{1}{2}(10 \quad x) \text {. } \\ \text { M. } y=\frac{1}{2} \times 10 \times \frac{1}{2}(10-x) \\ +\frac{1}{2}\left[10 \cdots \frac{1}{2}(10-x)+x\right] \times 10 \\ =5 x+50 \\\end{array}$