Concept:
A line parallel to x-axis has direction vector:
\[
(1,0,0)
\]
Step 1: Write symmetric form.
General form:
\[
\frac{x-a}{l} = \frac{y-b}{m} = \frac{z-c}{n}
\]
Step 2: Substitute direction ratios.
\[
l=1,\; m=0,\; n=0
\]
\[
\Rightarrow \frac{x-a}{1} = \frac{y-b}{0} = \frac{z-c}{0}
\]