A has exposed curved cylinder area \(2\pi(2R)(5R)=20\pi R^2\), hemisphere area \(2\pi(2R)^2=8\pi R^2\), and bottom disc \(\pi(2R)^2=4\pi R^2\). Thus its total is \(32\pi R^2\).

B has total area \(\pi Rx+\pi R^2\). Equate: \(32\pi R^2=\pi Rx+\pi R^2\), so \(31R^2=Rx\). Since R is a positive radius, divide by R to get \(\boxed{R=x/31}\).