.
All you need to know is the distance from the given point to the given line.
For it, use the lesson
- The distance from a point to a straight line in a coordinate plane
in this site.
Also, you have this free of charge online textbook in ALGEBRA-II in this site
ALGEBRA-II - YOUR ONLINE TEXTBOOK.
The referred lesson is the part of this online textbook under the topic
"The distance from a point to a straight line in a coordinate plane".