Which equation represents a line which is perpendicular to the x-axis?

or

step-by-step explanation:

we need to solve for 'x' the following equation:  

we have that:

⇒

⇒ ⇒

factorizing, we get that:

  ⇒

then, the solutions are: or

nothing extraneous has been found!

it's undefined because anything multiplied by 0 is 0. that said, 7 days is 168 hours