4. The rectangles $S_{1}$ and $S_{2}$ are drawn on a set of coordinate axes. $S_{1}$ has vertices at $(0, y) ;(x, y) ;(x, 4)$; and $(0,4)$, where $x<9$ and $y<4$. $S_{2}$ has vertices at $(x, 0)$; $(9,0) ;(9, y)$; and $(x, y)$. The rectangles are equal in area. What is the value of $\frac{360 x}{y}$ ?