First let's calculate the absolute error by subtracting both values:
[tex]20.9-12.2=8.7[/tex]So the absolute error is 8.7 millions.
Now, in order to find the percent error, we just need to divide the absolute error by the number of games sold:
[tex]\frac{8.7}{12.2}=0.7131=71.31\text{\%}[/tex]So the percent error is 71.31%.