Consider points a=(−10,−4) and c=(8,5). the point b is on the line passing through a and c. the x-coordinate of b is −1. determine the y-coordinate of the point b.

(-10,-4),(8,5)
slope = (5 - (-4) / (8 - (-10) = (5 + 4) / (8 + 10) = 9/18 = 1/2

y = mx + b
slope(m) = 1/2
(8,5)...x = 8 and y = 5
now we sub and find b, the y int
5 = 1/2(8) + b
5 = 4 + b
5 - 4 = b
1 = b
so the equation of line AC is : y = 1/2x + 1

so B is on the line...it has an x coordinate of -1...so its points are (-1,y)...and if it is on this line, it will follow the equation.

y = 1/2x + 1when x = -1
y = 1/2(-1) + 1
y = -1/2 + 1
y = 1/2 <=== the y coordinate