When you have two more equations, each containing two or more variables, you have Systems of Equations.

Example 1 (a set of two equations, each with two variables)

$$3x-5y=28$$

$$7x+10y=-5$$

Example 2 (a set of three equations, each with three variables)

$$3x-5y+4z=28$$

$$7x+10y-z=-5$$

$$-4x+y+z=19$$

NOTE: Systems of equations are solvable if the number of variables in each equation equals the number of equations in the set. For example, to solve a system of four equations, each equation would need to contain the four variables in question. And the equations cannot be equivalent or inconsistent (for example, $x + y = 2$ and $2x + 2y = 4$ are the same thing, while $2x + 2y = 5$ would be inconsistent as it's impossible for the two statements to be true at the same time).