There are four letters available to make up a car number plate, W, X, Y and Z. The number plate must have only three letters, but they can be placed in any order. How many different number plates can you make?​

You are driving directly behind a pickup truck, going at the same speed as the truck. a crate falls from the bed of the truck to the road. (a) will your car hit the crate before the crate hits the road if you neither brake nor swerve? (b) during the fall, is the horizontal speed of the crate more than, less than, or the same as that of the truck?