Speed=distance/time maths question. please help?

We know that for 20 minutes she ran at 9 miles per hour. That's 9 miles in 60 minutes. Dividing by 3 will give us how far she ran in 20 minutes. So she ran 3 miles in 20 minutes. She ran another mile in the last 10 minutes, for a total of 4 miles in 30 minutes. Multiplying by 2 will give us the number of miles ran in an hour. So 8 miles in 60 minutes. Thus she ran an average of 8 mph.