1. When K>0, the linear function increases monotonically.

So x =-3, y =-5; x=6，y=-2

Namely: {-5=-3k+b

-2=6k+b

Solution: k= 1/3, b=-4.

So: y= 1/3x-4.

2. when k

So x=-3, y =-2; x=6，y=-5

Namely: {-2=-3k+b

-5=6k+b

Solution: k=- 1/3, b=-3.

So: y=- 1/3x-3.

In a word: when K>0, y= 1/3x-4.

When k < O, y=- 1/3x-3.