A frog can jump over a point in the following way: if a frog at point $M$ jumps over point $N$, it lands on the point of reflection of point $M$ over $N$. A frog is initially at point $X$. $A$, $B$, $C$ are points such that $X$, $A$, $B$ and $C$ are on the same plane. The frog first jumps over $A$, then over $B$, then over $C$, and then continues to jump over point $A$, $B$ and $C$ alternately. Suppose $XA = 36$ cm, $XB = 84$ cm, $XC = 48$ cm. After $2021$ jumps, the frog is at point $Y$ . $XY = k$ cm. Enter $k$.