Answer
For $2010\Rightarrow 140.6\; bu/acre$
For $2004\Rightarrow 160.3\; bu/acre$
Difference$=19.7\;bu/acre$.
Work Step by Step
In $2010$ $\Rightarrow 12.4\;billion\;bu$ from $88.2\;million\;acres$.
In $2004$ $\Rightarrow 11.8\;billion\;bu$ from $73.6\;million\;acres$.
Divide $bu$ value by $acre$ value.
For $2010$
$=\frac{12.4\;billion\;bu}{88.2\;million\;acres}$
$=140.589569161\; bu/acre$
$=140.6\; bu/acre$
For $2004$
$=\frac{11.8\;billion\;bu}{73.6\;million\;acres}$
$=160.326086957\; bu/acre$
$=160.3\; bu/acre$
Difference in yield
$=160.3\;bu/acre - 140.6\;bu/acre$
$=19.7\;bu/acre$.
