1) because m∠ABE = m∠CBD, so any rotational transformations between these two angles will still make them equal.
2) Expand 3(x - 4) = 33
3x - 12 = 33
3x = 44
== 3x + 0 = 44
Having (+ 0) on the LHS does not change the equation in any way.
3) Expand 3(x - 4) = 33
3x - 12 = 33
3x = 33 + 12
3x - 12 + 12 = 33 + 12
Having (-12 + 12) on the LHS does not change the equation in any way, as (-12 + 12) is just 0.
4) Expand 3(x - 4) = 33
3x - 12 = 33
These two equations are equal, except the original equation is factorised, for simplicity's sake.
5) because m∠ABE = m∠CBD
The sum of the angles between m∠ABE is going to be equal to the sum of the angles between m∠CBD.