25.A straight one-mile stretch of highway,40 feet wide,is closed.Robert rides his bike on a path composed of semicircles as shown.If he rides at 5 miles per hour,how many hours will it take to cover the one-mile stretch?( )
Note:1 mile=5280 feet
一段直線的公路,長一英里、寬40英尺,被封閉了。Robert騎自行車走的路線是由如圖所示的半圓組成的。如果他以5英里每小時(shí)的速度騎行,他需要多少小時(shí)才能走完這一英里的路段?( )
注:1英里=5280英尺。
?