Khan Academy Solving systems with substitution 552 03:43
Khan Academy Solving systems with substitution 537 05:57
Khan Academy Solving systems with substitution 577 03:43
Khan Academy Solving systems with substitution 508 04:38
Khan Academy Solving systems with substitution 584 06:03
Khan Academy Solving systems with substitution 532 04:05
Khan Academy Solving systems with substitution 578 04:20