6.3 Video - Simplest Form
https://www-k6.thinkcentral.com/content/hsp/math/gomath/common/video/video.html#videoId=ref:En_575
6.4 - Common Denominators
https://www-k6.thinkcentral.com/content/hsp/math/gomath/common/video/video.html#videoId=ref:En_972