The arithmetic sequence is .
Find the common difference by subtracting successive terms.
\The common difference is 7.
\Add 7 to last term of the sequence to get the next termin the sequence.
\Continue adding 7 untill the next three terms are found.
\28 + 7 = 35, 35 + 7 = 42 and 42 + 7 = 49.
The next three terms are 35, 42, 49.