Complete the following subtraction exercises. 10 – 2 = 14 – 6 = 15 – 9 = 17 – 8 = 13 – 5 = 11 – 8 = 20 – 8 = 16 – 7 = 12 – 9 = 21 – 9 = 11 – 6 = 5 – 5 = 4 – 0 = 16 – 8 = 10 – 5 = 18 – 7 = 13 – 8 = 12 – 4 =