[填空题]
A roller coaster reaches the top oh(mna;07ku s l-xp ex50p9gim f the steepest hill with a s/ap6jts: hfx5 *grj mabyw:5- -xom)j peed of 6.0$ \mathrm{~km} / \mathrm{h}$ . It then descends the hill, which is at an average angle of 45$^{\circ}$ and is 45.0 m long. What will its speed be when it reaches the bottom? Assume $\mu_{\mathrm{k}}$=0.18 km/h
