Thank you, pdurrant, I love trying these puzzles.
Spoiler:
Start --- ?/16 pt + 0/7 pts + 0/3 pts
1-- pour the ?/16pt into the 0/7pt
now have-- ?/16 pt + 7/7 pt + 0/3pt
2-- pour the 7/7pt into the 0/3pt
now have-- ?/16 pt + 4/7pt + 3/3pt
3-- pour the 3/3pt into the ?/16pt
now have-- ?/16pt + 4/7pt + 0/3pt
4-- pour the 4/7pt into the 0/3pt
now have-- ?/16pt + 1/7pt + 3/3pt
5--pour the 3/3pt into the ?/16pt
now have-- ?/16pt + 1/7pt + 0/3pt
6-- pour the 1/7pt into the 0/3pt
now have-- ?/16pt + 0/7pt + 1/3pt
7--pour the ?/16pt into the 0/7pt
now have-- ?/16 pt + 7/7pt + 1/3pt
8-- pour out the ?/16 pt
now have-- 7pts + 1 pt + 8pts (one gallon)
Hopefully, I got it the first time this time.