The stopping distance d of an automobile is directly proportional to the square of its speed v. A car required 45 feet to stop when its speed was 60 miles per hour. Find a mathematical model that gives the stopping distance d in terms of its speed v. It also wants me to do this problem ---->( Estimate the stopping distance if the brakes are applied when the car is traveling at miles per hour.)

Alright so whenever you see the words directly proportional, it always means something equals something else multiplied by a constant. Usually we call this constant k. So it says the stopping distance d of the car is directly proportional to the speed v of the car. Thus we write this as d = kv. It says it takes 45 feet to stop at 60 miles per hour. So 45 = 60k so k = 0.75. Thus d = 0.75v. I think you forgot to to put the other part in miles per hour but all you need to do is plug it into the formula to get d. Just remember that the units are different on both sides. Hope this helps