Find 4 on the x-line (the horizontal line).
Find where the red line crosses through that is where the 4 is at.
Once you find it, trace the line in which the 4 is x, and find the y.
The line gives (4, -1)
Find the slope of the line.
(4, -1) = (x₁ , y₁)
(0, 2) = (x₂ , y₂)
slope = (y₂ - y₁)/(x₂ - x₁) = (2 - (-1)/(0 - 4) = 3/-4
y = (-3/4)x + b
Plug in a point, for example (0, 2)
2 = (-3/4)0 + b
Simplify
2 = 0 + b
b = 2
Plug in 2 for b
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f(x) = (-3/4)x + 2 is your equation.
Now, plug in 4 for x (as you are solving for x.
f(x) = (-3/4)(4) + 2
Simplify
f(x) = -3 + 2
f(x) = -1
-1 is your function when x = 4
hope this helps
