Answer:
a = 0, 3, 6, 9
Step-by-step explanation:
The divisibility rule for 3 is that the sum of the digits is equal to a number that is divisible by 3.
Example
67821 is divisible by 3 because 6 + 7 + 8 + 2 + 1 = 24, which is evenly divisible by 3.
We have 2 + 1 + 5 + a + 4 = a number divisible by 3
2+1+5+4 = 12.
Therefore, a can equal 0, 3, 6, or 9.
Hope this helped!
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