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 hang a book bag on a spring scale and place the bag on a platform scale so that the platform scale reads 23.7n and the spring scale reads 13.8n. what is the magnitude of the force that earth exerts on the bag?