Answer:
60 miles/hour
Explanation:
I'm not a hundred percent, but half the miles you'd go in an hour would e 20. Cause 40 divided by 2 (Half) is 20. So you'd put 40 miles first, cause that's how much there is in an hour, and then you add 20 miles, cause it's half of an hour and half of 40. I'm sorry if this doesn't make sense, I tried my best, lol.