Since this is the equation of a straight line, there are no restrictions on what you could choose for a value of x. In "official" terms, we say the domain of the function is all real numbers.
Say you pick something simple like x=1. Now, insert this value, and the equation becomes
2−7=y
or y=−5
This means (1,−5) must be a point on the line, and it is also an ordered pair that satisfies the equation.
