y =
x + 4
the equation of a line in slope- intercept form is
y = mx + c ( m is the slope and c the y-intercept )
to calculate m use the gradient formula
m = (y₂ - y₁ ) / (x₂ - x₁ )
with (x₁, y₁ ) = (0, 4 ) and (x₂, y₂ ) = (-3, 0 ) ← 2 points on line
m =
=
= 
the line crosses the y-axis at (0, 4 ) → c = 4
y =
x + 4 ← in slope-intercept form