9. (10 points) As shown in the figure, a rectangular prism with length, width, and height of $15, 5, 4$ has a smaller rectangular prism with length, width, and height of $y, 5$, $x$ (where $x, y$ are integers) cut out from it. The remaining volume is 120. Find $x$ and $y$.


【Analysis】According to the problem, we can get the equation: the volume of the large rectangular prism - the volume of the cut-off small rectangular prism $=$ the volume of the remaining part, then list the indeterminate equation according to the volume formula of the rectangular prism and solve it.

【Solution】According to the problem, we have
$$
15 \times 5 \times 4-y \times 5 \times x=120 \text {, }
$$

Simplifying, we get: $x y=36$,
$$
36=1 \times 36=2 \times 18=3 \times 12=4 \times 9=6 \times 6,
$$

Since $x, y$ are integers, and $x<4, y<15$,
so $x=3, y=12$.
Answer: $x=3, y=12$.