84. As shown in the figure, Jia and Yi are two cylindrical containers, with the ratio of their base areas being $2: 3$. In the Jia container, there is an iron ball with a volume of 30 cubic centimeters, at which point the water levels in the two containers differ by $x$ centimeters; if the iron ball is moved from the Jia container to the Yi container, the water levels in the two containers still differ by $x$ centimeters. If the base area of the Jia container is 25 square centimeters, $x=$ $\qquad$ cm.
Reference answer: 1