The slope intercept form for a line is y = mx + b.
↑ ↑
m is the slope of the line or how steep it is. b is where the line runs into the y axis at one point. x and y are the values you plug in when you have a specific point you want to use (x, y).
For the first picture, you can see that the line "intercepts" or collides with the y axis at 1. Thus we know the b value.
To find the slope, you just pick 2 points on the line and plug them into a little equation (try to memorize this equation, it helps to find slope):
m = (y₂ - y₁)/(x₂ - x₁)
The two points we'll use are (1, 0) and (0, 1) since x goes through both of
those points. ↑ ↑ ↑ ↑
x₁ y₁ x₂ y₂
m = (1 - 0)/(0 - 1)
m = 1 / -1
m = -1
This makes sense - since the slope is going downward, the slope is negative.
So the equation is:
y = -x + 1
____________________________________________________________
For the second problem, We can see the line intercepts the y-axis at -5. That is our b value.
The the slope of this line is 0 since it is not going up or down, so that is our m value:
y = 0(x) - 5 = -5
The equation of the line is y = -5