Calculus differentiation word problem?

At 7:00 a.m. a truck is 100 miles due north of a car. The truck is traveling south at a constant speed of 40 mph, while the car is traveling east at 60 mph. How fast is the distance between the car and the truck changing at 7:30 a.m.?


From your highschool geometry & algebra, whats the distance between the truck & car at time t ? Answer this and we shall proceed.