Answer :
9 pencils
12 pens
21 -3 = 18
18 / 2 = 9
9 + (9+3) = 21
9 + 12 = 21
21 = 21
answer checks out.
12 pens
21 -3 = 18
18 / 2 = 9
9 + (9+3) = 21
9 + 12 = 21
21 = 21
answer checks out.