# Counting triangles and lines

Consider 8 vertices of a regular octagon and its center. If $$T$$ denotes the number of triangles and $$S$$ denotes the number of straight lines that can be formed with these 9 points, then the value of $$T-S$$ is a 2-digit integer $$\overline{ab}$$. Find the value of $$a+b$$.

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