Quadrilateral ABCD has a 90 degree right angle at C and BC = CD = 10 miles. A car is traveling from A to C. If the car takes the path of AC then it takes 30 minutes. If the car takes the path of AB then BC it takes 35 minutes. If the car takes the path of AD and then DC it takes 40 minutes. The car always travels at a constant speed. What is the speed of the car?