Using the 2-point form of the equation for a line, you can write the equation as
y = (y₂ -y₁)/(x₂ -x₁)×(x -x₁) +y₁
If we let (x₁, y₁) = (4, 2) and (x₂, y₂) = (9, 12) this becomes
y = (12 -2)/(9 -4)×(x -4) +2
y = (10/5)×(x -4) +2
y = 2x -6
The equation in slope-intercept form of the given function is ...
y = 2x -6