You need to find two things: the gradient of the line and a point on the line.

Get those two things and substitute into the general equation

where m is the gradient and is a point on the line.

The point on the line is given on a platter. It's (5, 4).

As for the gradient, you know that it'sperpendicularto the line .

Therefore:

(You do know that when two lines are perpendicular, the product of their gradients is equal to -1, right?)