John gets $10 per hour and Sally makes $12.50 per hour so Sally makes $2.50 more then John per hour.
We can tell John makes $10 per hour because we divid how much he made by the amount of hours it took to make to get 10 and we did the same thing for Sally ($50/4=12.5) and then we subtract Sally's pay per hour by John's pay per hour to see how much more Sally makes per hour.
I hope that helped and made sense. :)