请教一道路程题。谢谢！

usyd

请教一道路程题

Q: it a motorist had driven 1 hour longer on a certain day and at an average rate of 5 miles per hour faster, he would have covered 70 more miles than he actually did. How many more miles would he have covered than he actually did if he had driven 2 hours longer and at an averge rate of 10 miles per hour faster on that day?

The way i did it:

设actually did的时候的hour是x, average speed是y

(x+1)(y+5)=70+xy 那么5x+y=65

现在问(x+2)(y+10)-xy等于多少 将上面代入就得150

但答案是can not be determined.....不解。请教！谢谢！