If 3x +  5 = 8x, then x=1, not x=-1.  The mistake was made when she said that 8x-3x=-5x, which is not true.

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if you look she actually says -3x from 8x but writes -5x from 8x and then somewhere got lost and answered with -1=x your right with x=1 kinda tossed me for a loop there a bit glad I'm not the only one who noticed