01. WHOLE NUMBERS
Explanation:
23
Solution:
Here, (31 + 15) + x = 31 + (15 + 23).
But, by associativity of addition,
We have (31 + 15) + 23 = 31 + (15 + 23)
So, comparing (31 + 15) + x = 31 + (15 + 23) and (31 + 15) + 23 = 31 + (15 + 23),
We have x = 23
Hence, the correct option is (c).