Not necessarily. You could have done your multiplication wrong. Or in some cases, yes, you could have to use another skill. For example, you can't solve an optimization problem with addition, you need some calculus skills under your belt.
He can conclude that the system of equations has no solution since one equation in it always results with false equivalency.
Hope this helps.
r3t40
Multiply first then you would wanna add but you can't until you subtract 5-3 then add I got 12
