it depends on the situations
some situations two unknown is likely to solve the x and the y
and it is more likely many equations given with only x and y variable are given
for two unknown variables it only takes up to two equations to solve the x and y
so you need an algebraic skills like an animal to solve the equations given, by any method that you like.
methods are
substitution
where you in terms the another variable to another variable from either first or second equation given
then substitute it to the remaining equation then you can come up to the answer to the first variable then substitute it from the rest
elimination
where you subtract the two equation and eliminate the one variable by multiplying the equation that you choose with the factor that can make the difference of the two same variable to zero then comes up the answer of the first value then back to substitution then substitute to solve the remaining variable
last is
by matrix method
it is a long process and you will learn it when you are in higher years
