Slope = rise/ run or (y1-y2) / (x1-x2)
for the first two points
slope = (4-3) / (2-6) = - 1/4
for the second and third points we need slope = -1/4 , then solve for c
(3-c) / (6-(-5) ) = -1/4
3-c = -1/4(11)
3-c = -11/4
3+11/4 = c
23/4 = c or 5 3/4 or 5.75