Combinations

Step 1: Understand the number of straight lines.
The total number of straight lines that can be formed by 15 points (if no three points are collinear) is given by , which is the number of ways to select 2 points out of 15.
Step 2: Account for the collinear points.
6 of the points are collinear, meaning they lie on the same straight line.
The number of straight lines that can be formed by any two of these 6 points is .
Step 3: Subtract the overcounted lines.
Since the lines formed by these 6 points have been counted twice, we subtract from the total number of lines.
Step 4: Conclusion.
The correct number of straight lines is , which corresponds to option (b).