What does K=? Someone please help.

(10,2) is 3 to the right of x = 7, so in order for x = 7 to bisect our segment, (k,2) must be 3 to the left of x = 7. In other words, it must be at (4,2)
So k = 4
We can immediately conclude that this is a horizontal line, because both of the y positions are 2.
A perpendicular bisector, or the point in the middle of said line, is provided as x=7, and since we have concluded that this is a horizontal line, the mid-point is (7,2).
We can use this to find the x-value of b (or k), by finding the distance between a point A (10,2), and a mid-point (7,2).
The distance from 7 to 10 (and vice versa) is the absolute value of 3, and the point A(X) is great than Mid(X), so we will be subtracting to get B.
Since we have a midpoint, to find B(K) all we have to do is subtract the distance from A(X) to Mid(X) from Mid(X).
Mid(7) - 3 = 4
B = B(4,2)
K = 4