In this edition of “CBS This Morning’s” Pushing the Limits series, we met two high school students who not only conquered calculus, but also pulled off an achievement that can stump college professors. Of more than 302,000 students around the world who took the Advanced Placement calculus test last year, Landon Labuske and Cedrick Argueta were two of only 12 who achieved a perfect score. Chip Reid reports.