7x-29-21x=3-(12+2x)
7x - 21x - 29 = 3 - 12 + 2x place common terms together
-14x - 29 = -9 + 2x combine the x terms on the left and the ones terms on the right
-29 = -9 + 2x + 14x add 14x to both sides
-29 = -9 + 16x
-29 + 9 = 16x add 9 to both sides
-20 = 16x
x = -20/16 = -5/4 or -1.25