Diana usually drives at average rate of 30 mph. If Diana is able to increase her average rate by 10 mph, how many minutes would it take her to get to Tony's house?

It would take Diana 18 minutes

Step-by-step explanation:

Diana's average rate is 30 miles per hour and if you add 10 miles per hour to that you get 40 miles per hour.  Since there are 60 minutes in an hour, divide 60 by 40 (the speed she travels) to find the distance traveled per minute.  You end up getting 1.5 miles per minute as your rate.  Take the total distance (12 miles) times the speed rate per minute (1.5 miles per minute) to find how long it would take to travel the distance.  The answer is 18 minutes