You need to find the volume of extra space. The space has the shape of a right rectangular prism.
The formula for the volume of a right rectangular prism is
[tex]V=A\cdot h[/tex]Where A is the floor area and h is the height of the ceiling
If Maggie puts a 7 ft ceiling then the volume of the space will be
[tex]V1=3000ft^2\cdot7ft=21000ft^3[/tex]But if she puts an 8 ft ceiling instead, the volume will be
[tex]V2=3000ft^2\cdot8ft=24000ft^3[/tex]Then the extra space she will have to heat and cool will be
[tex]V2-V1=24000ft^3-21000ft^3=3000ft^3[/tex]Maggie will have to heat and cool 3000 ft³ more of space if she puts an 8 ft. ceiling