Jenny,
I believe the 7-7 is 7 YRS AND 7 months from 1771 so he would be 21 after that time , ie in 1778/9
By the same method the second would be 21 in 1809.
Dave
Jenny, it is worth adding that for neither of these apprentices is there a record that they purchased their freedom at the end of their apprenticeships. This means that neither of them found it necessary to purchase a trade mark
Dave