The first three terms of an arithmetic sequence are as follows.

Answer:
9, 3
Step-by-step explanation:
To get from 27 to 21, you subtract by 6. To get from 21 to 15, you must also subtract by 6. Therefore, subtracting by 6 is the pattern. In order to get the next number in the sequence, we must subtract 6 from 15.
15 - 6 = 9
The next number is 9. To find the number after 9, we must do the same thing - subtract 6 from 9.
9 - 6 = 3
The 5th number of the sequence is 3.
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