Question 63
A blacksmith is building a horizontal iron fence made of parallel vertical bars, each $18\,\mathrm{cm}$ from its two neighbors. He joins the top ends of each adjacent pair with a circular arc in the plane of the bars. Its highest point is $3\sqrt3\,\mathrm{cm}$ above the dashed line through all bar tops, perpendicular to the bars. How long is each curved bar used for an arc?
(A) $8\pi(\sqrt3-1)\,\mathrm{cm}$; (B) $6\pi\sqrt3\,\mathrm{cm}$; (C) $12\pi(\sqrt3-1)\,\mathrm{cm}$; (D) $4\pi\sqrt3\,\mathrm{cm}$; (E) $8\pi\sqrt3\,\mathrm{cm}$.
(A) $8\pi(\sqrt3-1)\,\mathrm{cm}$; (B) $6\pi\sqrt3\,\mathrm{cm}$; (C) $12\pi(\sqrt3-1)\,\mathrm{cm}$; (D) $4\pi\sqrt3\,\mathrm{cm}$; (E) $8\pi\sqrt3\,\mathrm{cm}$.