You may want to review equations first.

A system of equations is a list of equations, *all* of
which have to be true. Generally, they'll have more than one
letter in them. For example, *y* = −2 and *y* = 1
− 2*x* are *one* system of equations.

A solution of the system is a pair of values for *x*
and *y* that makes both of the equations true. For example, a
solution of the system above would be (3 ⁄ 2,
−2), because when you substitute in
3 ⁄ 2 for *x* and −2 for *y*
both equations are right.

Just like with one equation, the equations in a system don't have
to have both letters in them. For example, in the system we used
as an example, one equation didn't have an *x*. It would even
be okay if one or both equations had no letters at all. Just
substitute in the values of *x* and *y* wherever you see
them. If the equations are both right, then they're a solution;
if even one is wrong, then they're not.