4. The gray rabbit and the white rabbit set off from their homes along the same road to go to each other's home. The white rabbit rests once every 30 meters, and the gray rabbit rests once every 20 meters. They meet at the midpoint and rest at the same time. If the gray rabbit rests 15 more times than the white rabbit when they meet, then the distance between their homes is $\qquad$ meters.
\begin{tabular}{c}
4 \\
\hline 1800
\end{tabular}