If the lines 2x+3y+12=0 and y=mx+1 meet at a point whose coordinates are equal, what must m equal? The hard part is not the answer I already have it. I just don't understand some of the steps it shows

The point on the first line with equal coordinates is found from 2x+3x+12=0 (if we substituted y for x+1. Wouldn't there be a three somewhere? after substituting y for x, so 5x+12=0 and x=y=-12/5.
Then -12/5=(-12/50m+1 so m+(-5/12)(-12/5-1), from which m = 17/12