General Solution of Diophantine equation Having the equation:

$$35x+91y = 21$$

I need to find its general solution.
I know gcf $(35,91) = 7$, so I can solve $35x+917 = 7$ to find $x = -5, y = 2$. Hence a solution to $35x+91y = 21$ is $x = -15, y = 2$.
From here, however, how do I move on to finding the set of general solutions? Any help would be very much appreciated!
Cheers

Hint: If $35x + 91y = 21$ and $35x^* + 91y^* = 21$ for for some $(x,y)$ and $(x^*, y^*)$, we can subtract the two equalities and get $5(x-x^*) + 13(y-y^*) = 0$. What does this tell us about the relation between any two solutions?
Now, $5$ and $13$ share no common factor and we're dealing with integers, $13$ must divide $(x-x^*)$. In other words, $x = x^* + 13k$ for some integer $k$ and substituting it into the equality yields $y = y^* - 5k$. Thus, once you have one solution $(x^*,y^*)$, all of them can be expressed as $(x^*+13k, y^*-5k)$.
