James gets bored with his game so decides to play a different one.  That game promises 100 hours of gameplay but 80% of that is boring grinding.  However, the expansion does add another 30 hours of enjoyable gameplay.  How much enjoyable gameplay does James get?
The first game was 100*.8=
<gadget id="calculator">100*.8</gadget>
<output>80</output>
80 hours of grinding.
So it was 100-80=
<gadget id="calculator">100-80</gadget>
<output>20</output>
20 hours of good gameplay.
The expansion brought the time of good gameplay to 20+30=
<gadget id="calculator">20+30</gadget>
<output>50</output>
50 hours.

<result>50</result>