Some books say while back solving/plugging start with choice D and E.
Largely one of them seem to correct answer !! (survey says)

So start with D here...

0.7 of 150 = 105
Now 80% first 100 games is 80 games; and 50% of remaining 50 games is 25.Now together they make 105 games.

You could also use simple algebra:

80 +.5n/100 + n = 70/100, because the first part represents 70 percent of the total (100 + n) which is 100 percent of the games played.

Cross multiply to get:

70n + 7000 = 8000 + 50n

n = 50

100 + 50 = 150 total games played.

Also, just an aside, this is a Problem Solving question, and you should post it in the problem solving section instead of the Data Sufficiency section of the forum.