Hey mcolula.
What is covered in your notes?
If you want to get some notes and algorithms, the subjects you need to look at include bi-linear diophantine equations, and the Chinese remainder theorem.
Hello, mcolula!
If you truly "don't understand too much of it",
. . my explanations won't help you at all.
We have: .
Then: .
Since is an integer, must be a multiple of 7.
. . .[3]
Since is an integer, must be a multiple of 3.
. . This happens when
Substitute into [3]: .
Substitute into [2]: .