Chapter 10 - Section 10.6 - Radical Equations and Problem Solving - Exercise Set - Page 732: 72

7.295 feet

$P=2\pi*\sqrt {I/32}$ $3=2\pi*\sqrt {I/32}$ $3/2\pi=2\pi*\sqrt {I/32}/2\pi$ $3/2\pi=\sqrt {I/32}$ $(3/2\pi)^2=(\sqrt {I/32})^2$ $(3/2\pi)^2=I/32$ $9/4*\pi^2=I/32$ $32*9/4*\pi^2=32*I/32$ $8*9/\pi^2=I$ $72/\pi^2=I$ $72/9.8696=I$ $7.295 = I$