If the line is perpendicular to x = 4, then that means the answer should be y = some number
and since we have the equation going through point (5,7), we look at the y-value since our equation is y=some number and replace the y-value into that equation.
Since there are infinite possible answers we will just make our way through the given answers.
A: Imagine the line for the equation Y=4, it is a straight horizontal line going through every value of x but only one value of Y because it doesn't get any higher or lower. So Y=4 can not be the answer because Y never = 7.
B: Do the same thing and imagine this line. It is a vertical line on the point of X = 5. This one does cross though (5,7) but it is not perpendicular to X= 4 so is not the answer.
C: Crosses through (5,7) and is perpendicular to x = 4. correct answer.