Substitution Method
Video:https://www.youtube.com/watch?v=j7kaNtzKiMU
Tutorial: http://www.phschool.com/atschool/academy123/english/academy123_content/wl-book-demo/ph-231s.html
Practice Now: http://www.regentsprep.org/Regents/math/ALGEBRA/AE3/PracAlg.htm
Quiz: http://www.phschool.com/webcodes10/index.cfm?fuseaction=home.gotoWebCode&wcprefix=ata&wcsuffix=0702
Practice: https://www.opened.com/assessment/show-equality-of-substitution-with-equations/1069424