I'm afraid you're a bit off. A location in 3-dimensional space must be described by three variables. But a position on a line requires only one variable. A position on a plane requires two variables. So, if you're talking about a line, how many equations must you have in order to knock down the number of variables from 3 to 1? If you're talking about a plane, how many equations must you have in order to knock down the number of variables from 3 to 2?