First Question:
[tex]\frac{1}{4}(8-6x+12) = [/tex]
[tex]\frac{8}{4}-\frac{6x}{4}+\frac{12}{4} = [/tex]
[tex]2-\frac{3}{2}x+3 = [/tex]
[tex]\boxed{(D) -\frac{3}{2}x+5}[/tex]
Second Question:
The average (mean) rate of change is just [tex]\dfrac{-378}{7} =\boxed{-54 ft/min} [/tex]
Hope this helps :D