



 
Hi John, The circumference of a circle is given by $\pi$ times the diameter. Suppose the inside diameter is $d$ feet. Then, since the thickness of the wall is $7$ inches which is $\large \frac{7}{12}$ feet, the outside diameter is \[d + 2 \times \frac{7}{12} \mbox{ feet.}\] But the outside circumference is 118 feet and hence \[\pi \left( d + 2 \times \frac{7}{12} \right) = 118\] and thus \[ d + 2 \times \frac{7}{12} = \frac{118}{\pi}.\] Finally \[d = \frac{118}{\pi}  2 \times \frac{7}{12} = 36.4 \mbox{ feet.}\] Penny  


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