First let's find the slope of line joining (2, 5) and (4, 4)
Assuming points (x₁, y₁) and (x₂, y₂)
Slope = (y₂ - y₁) / (x₂ - x₁)
Slope = (4 - 5) / (4 -2) = -1/2 = -0.5
From equation of line: y = mx + c
y = -0.5x + c
Using the point (2 , 5) as passing through y = -0.5x + c
x = 2, y = 5
5 = -0.5*2 + c
5 = -1 + c
5 + 1 = c
6 = c
c = 6
Therefore the y-intercept which is c = 6
y-intercept = 6
Hope this explains it.