The solution set of y2 6 5y is 2 3 because 22 6 5 2 and 32 6 5 3. The solution set of the single equation is the set 0. Solve 2x 3 7 where x is a natural number.
If x 72 then y 0.
Lets try some other numbers. A is a subset of B. We take all scalar multiples of A 3 1 B and then add the particular solution p A 3 0 B to each of these scalar multiples. That set is your answer.