-4 + -7= -11
When adding negative numbers if the are both negative then you add them. When you have a negative and a positive you subtract. In this problem they just took out the plus sign.
Answer:

To find this you must find the slope first:

which is, after performing some calculating is -2.
Next you need to set up your eqaution:

when you set it up, and substitute the variables for your slope and points you should get this:


add 2 to both sides

subtract y from both sides
The answer to this question is 5.35