ignore #9 #10 and #11
i need help on #12 can someone please put what she did wrong?

Answer:
her answer is wrong, it must be 3x + 2
because:
(5x + 3) - (2x + 1)
= 5x + 3 - 2x - 1
= (5x - 2x) + (3 - 1)
= 3x + 2