If the xy-plane, a line contains the points (4,2), (-2,-1) and (k,5). What is the value of k?

A 6
B 7
C 8
D 9
E 10

Use the first two points to find the slope of the line.

\dfrac{y_2-y_1}{x_2-x_1}=\dfrac{-1-2}{-2-4}=\dfrac{-3}{-6}=\dfrac{1}{2}.

From there, you can either use the slope formula again to solve for k, or you can just count up and over from (4, 2). A line that goes through (4, 2) and has a slope of 1/2 will go like this:

(4, 2)
(6, 3)
(8, 4)
(10, 5)

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