#### Answer

about 55.56 feet squared

#### Work Step by Step

The given formula is $d=1.2\sqrt A$. We need to isolate $A$ in order to solve for it:
Divide by 1.2 on both sides and then square each side:
$(\frac{d}{1.2})^{2}=A$
Now, plug in 8 for $d$ and then repeat for $12$:
$(\frac{8}{1.2})^{2}=44.44$ and $(\frac{12}{1.2})^{2}=100$
Subtract the area when $d=12$ by the area when $d=8$:
$100-44.44=55.56$