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