Like in algebra, how would one solve for x and y in:

4xy = 1 mod 29

2xy^2 = 1 mod 29

Yeah, the solution is obvious and easy in this one, how about when adding or subtracting terms?

x^2-6y = 1 mod 210

3y^2+10y+12x = 1 mod 210

Which one would seem easier to solve?

For both of them, I would go for substitution algebraic method, since the only constant (of degree 0) we are dealing with here in both equations is 1. but I don't know any better. Any help, feedback, or similar equations are appreciated here. Thanks.