In an isothermal process, 0.1 cubic feet of standard air per minute (SCFM) is pumped into a balloon. Tension in the rubber skin of the balloon is given by \(\sigma=k A\), where \(k=200 \mathrm{lbf} / \mathrm{ft}^{3}\), and \(A\) is the surface area of the balloon in \(\mathrm{ft}^{2}\). Compute the time required to increase the balloon radius from 5 to 7 in.