To answer this question, we can use the explicit formula of an arithmetic sequence:

• We have that the first term (a1) of the arithmetic sequence is 6 (a1 = 6).
,
• The common difference is 3 (d = 3).
Then, we have that the formula is:

We can use this formula to find the 20th term of this arithmetic sequence as follows:

In summary, the formula for the arithmetic sequence is:

And the 20th term is equal to 63.