The given figure can be divided in two parts 1) Square with side 7 in 2) A right triangle with base 12 in and height 7 in.
1) Area of square = 
Side of the square is 7 in.
Area = 
2) Area of triangle = 
Area of triangle =
Area of polygon= Area of square+ Area of triangle
Area of polygon = 49+42 =91 square in.
Area = 
The question is basically asking you to calculate the new volume of the box that is 12x 7.5 x 2.5inches and to see if it has a larger volume than 162.5 sqin.
If you calculate the volume you should get 225 square inches.
You can calculate here and then subtract 25 I got $575.29 but see what you get.
The answer to "12x-(4y+7z) for x=9 y= 4 and z = 2" is 78.
