1. -28 = -7(3x + 4) + 21x
= -28 = -7 * 3x + -7 * 4 + 21x
= -28 = -21x - 28 + 21x
= -28 = -28 (ps. The reason that we took away both of the 21x’s is because when you have a positive and negative of the same exact number, then that becomes 0 so right now, we are just left with -28 = -28
2. -28 = -28
So, this is our final answer, glad I could help!