If slope = -1/3 and coordinates are (8,6) and (k,7) what is the missing coordinate

Slope = (y2 - y1) / (x2 - x1)
(8,6)...x1 = 8 and y1 = 6
(k,7)...x2 = k and y2 = 7
now we sub
(7 - 6) / (k - 8) = 1/-3

k - 8 = -3
k = -3 + 8
k = 5 < ur missing coordinate is going to be 5

The coordinates of point a right now is (-3,-1) you have to multiply these coordinates by a factor of 2 to get (-6,-2)

The total would be 40.53