It's only 40 minute's walk from the center of BeiJing by groundfloor,对划线部分提问

问题描述:

It's only 40 minute's walk from the center of BeiJing by groundfloor,对划线部分提问
only 40 minute's walk画线

only 40 minute's walk 说的是路途远近(只需步行……分钟),因此对路途远近提问,用how far,这个问句可以是这样:
How far is it from the center of Beijing.