问题描述：
我想问一道英文的数学题!.我要过程
John leaves home and start walking at 4 km/h to his friend's house. Half and a hour later, his sister Susan leaves the house on a bicycle and heads in the same direction at 12 km/h. How far away are they from the house when Susan catches up to John, and how long after John fist left the house? 要用方程来解答
最后的fist应该是 first
John leaves home and start walking at 4 km/h to his friend's house. Half and a hour later, his sister Susan leaves the house on a bicycle and heads in the same direction at 12 km/h. How far away are they from the house when Susan catches up to John, and how long after John fist left the house? 要用方程来解答
最后的fist应该是 first
问题解答：
我来补答展开全文阅读