Hi, there.
______
First off, let's remember the slope-intercept formula.

.
Here,
»
-> gradient
»
-> y-intercept
≊≊≊≊≊≊≊≊≊≊≊≊≊≊≊≊≊≊≊≊≊≊≊≊
We know that
»
-> -1
»
-> 1
So let's substitute these parameters!

Simplify.

Hope the answer - and explanation - made sense,
happy studying!!!