Collinear Points
Collinear points are the points that lie on the same line. To determine if three points are collinear, we can calculate the slope of the line formed by any two points and check if it is the same as the slope of the line formed by the other two points. If the slopes are equal, then the three points are collinear.

Calculating Slope
The slope of a line passing through two points (x1, y1) and (x2, y2) can be calculated using the formula:
slope = (y2 - y1) / (x2 - x1)

Determining if the Points are Collinear
Let's use the points (-8, 5), (-2, 4) and (5, a) to determine if they are collinear.

The slope of the line passing through (-8, 5) and (-2, 4) is:
slope = (4 - 5) / (-2 - (-8)) = -1 / 6

The slope of the line passing through (-2, 4) and (5, a) is:
slope = (a - 4) / (5 - (-2)) = (a - 4) / 7

Since the points are collinear, the slopes of the two lines should be equal. Therefore, we can set the two slope equations equal to each other and solve for a:
-1 / 6 = (a - 4) / 7
-7 = 6a - 24
6a = 17
a = 17 / 6

Therefore, the value of a is 17 / 6.

Final Answer
The value of a is 17 / 6.