a) 34 + 99 = ☐ + 34

13 + 297 = 297 + ☐

201 + 118 = ☐ + 201

b) 9 + ☐ = 9

61 + ☐ = 61

(24 + 8) + 12 = 24 + (8 + ☐)

8 + 6 + 4 = 8 + (6 + ☐)

63 + 37 + 98 = (63 + ☐) + 98

☐ + 0 = 87

☐ + 10 = 10

a) 34 + 99 = 99 + 34

13 + 297 = 297 + 13

201 + 118 = 118 + 201

b) 9 + 0 = 9

61 + 0 = 61

 (24 + 8) + 12 = 24 + (8 + 12)

8 + 6 + 4 = 8 + (6 + 4)

63 + 37 + 98 = (63 + 37) + 98

 87 + 0 = 87

0 + 10 = 10