(i) We need two points to draw a line.
∴ Total number of lines = 12C2 = 66
(ii) Lines are drawn passing through each pair of points.
∴ Lines from point D will pass through all the remaining 11 points.
∴ 11 lines pass through D.
(iii) We need three points to draw a triangle.
∴ Number of triangles = 12C3 = 220
(iv) To get the triangles with one vertex as C, we need two vertices from the remaining 11 vertices
∴ Number of triangles with vertex at C = 11C2
= \(\frac{11\times10}2\) = 55