I just published the playlist of video explanations to all of the math questions in the Decemeber 2014 ACT 72G test.

 
I just posted the video explanations to all of the math questions in the June 2014 ACT 72C test. The question number 49 and 55 were the most challenging ones in this test.

 
I just posted the video explanations to all of the math questions in the December 2013 ACT 71E test. The question number 57 and 59 were the most challenging ones in this test.