It really depends on the excerpt that you have been given. Is this the one? I found in somewhere on the Internet.
The Bridegroom's doors are opened wide,
And I am next of kin;
The guests are met, the feast is set:
May'st hear the merry din.'
If this is the excerpt you have, then the answer is simple - alternating tetrameter and trimester. Tetrameter means that there are 4 meters in one line, and given that one meter consists of two syllables, that would mean that there are 8 syllables in one line. Similarly, trimester means that there are 3 meters, or 6 syllables in one line.
