Can anyone explain why the answer is d and not a

Hello,

solution in picture

Some things you need to know:

1) You need to know how to convert standard form to slope y-int. form and slope y-int. form to standard form.

2) When two lines are parallel, the slopes are the same.

3) When two lines are perpendicular, the slopes are negative reciprocals of each other. (Or their product is -1)
    example: 3/4 --> -4/3.
                    3/4 * -4/3 = -12/12 = -1

4) To find the value of b, substitute the point into the equation.

5) Convert the equation to slope y-int. form to find the slope.

6) When a line has an undefined slope, the slope y-int. will look either like
    y = __ (forms horizontal line) or x = __ (forms vertical line).
    To find the perpendicular of these lines, turn y to x / x to y.
    To find the value of __, look at the point located in the line, so if x = ___
    passes through (5,3), then x = 5 because x = 5 in the point. So the
    equation would be x = 5.

Use online practice tests and other sources if you don't understand.