To solve this problem you must apply the proccedure shown below:
1. You have that:
-The length is [tex] x [/tex] feet.
- The width is [tex] y [/tex] feet.
- The height is [tex] z [/tex] feet.
2. The box has one base. The cost of the base is:
[tex] c1=4.20xy [/tex]
3. It has four sides. The cost of the sides are:
[tex] c2=2(0.75yz)+2(0.75xy)\\ c2=1.5yz+1.5xy [/tex]
The answer is: The total cost is [tex] c=c1+c2\\ c=4.20xy+1.5yz+1.5xy [/tex]