Khan Academy Solving systems with substitution 560 04:20

Khan Academy Solving systems with substitution 512 04:05

Khan Academy Solving systems with substitution 560 06:03

Khan Academy Solving systems with substitution 483 04:38

Khan Academy Solving systems with substitution 559 03:43

Khan Academy Solving systems with substitution 522 05:57

Khan Academy Solving systems with substitution 537 03:43