You may want to review finding intercepts first.

Sometimes, you might have to find a point on a line for *x*
= 3, say. If it were a 0 instead of a 3, then this would just be
asking for the *y*-intercept, and you'd know what to do; just
put 0 in for *x* and solve for *y*. In this case, it's
the same idea; just put a 3 in for *x* instead of a 0.

For example, if you have to find a point on 2*x* + *y*
= −1 with *x* = 3, you just put 3 in for *x*,
getting 6 + *y* = −1. Solving for *y* gives
*y* = −7, so your point is (3, −7).

If instead you wanted *y* = 3, you'd just put 3 in
for *y* instead of for *x*. In this case, you'd get
2*x* + 3 = −1, whose solution is *x* = −2;
so the point is (−2, 3).