slope intercept form:
y = mx + b
m = slope
b = y-intercept
the y-intercept is the place on the y-axis (vertical) where the line crosses. In this problem, the line crosses at (0,4), meaning the y-intercept is 4.
y = mx + 4
the slope is technically the rate of change (rise over run) bewteen points.
If you take the distance from point (-1,3) and (0,4) you get a slope of 1/1, or just 1
y = 1x +4
this could also be:
y = x + 4
(because the 1 is invisible but still there)