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

After dividing the equation by the $\gcd$, you get $5x + 13y = 3$, which is equivalent to $5x = 3\pmod {13}$. Solving, $x = 11\pmod {13}$. Substitute $x = 11 + 13t$ into the equation and get $y = -4 - 5t$ which is the complete solution.
