7.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
一段直线的公路,长一英里、宽40英尺,被封闭了。Robert骑自行车走的路线是由如图所示的半圆组成的。如果他以5英里每小时的速度骑行,他需要多少小时才能走完这一英里的路段?( )
注:1英里=5280英尺。