you have to multiply everything in the parentheses by 21, so your new equation is
42-21x+12x=44
then reduce your x's on the left side, so -21+12 is -9, so your next equation would be
42-9x=44
then subtract 42 from each side to get x by itself, so then you get
-9x=2
then divide each side by -9, so then x=2/-9!