An open-top box is to be constructed from a 6 foot by 8 foot rectangular cardboard by cutting out equal squares at each corner and the folding up the flaps. Let x denote the length of each side of the square to be cut out.

Question

An open-top box is to be constructed from a 6 foot by 8 foot rectangular cardboard by cutting out equal squares at each corner and the folding up the flaps. Let x denote the length of each side of the square to be cut out. 
1. Find the function V that represents the volume of the box in terms of x 
2.How do I graph this gfunction to show the valid range of the variable x.

One side of the box is 6 - 2x and the other is 8 - 2x. When folded up, the height of the side of the box will be x. 
V = x (8-2x)(6-2x) 
The range of x is from 0 up to 3. When x - 3, one of the box side lengths becomes zero, and so does the volume. 
Make your graph of V vs x in the usual way.