Given six line segments of length 2, 3, 4, 5, 6, 7 units, the number of triangles that can be formed by these segments is
$(A)^6C_3 – 7$
$(B)^6C_3 – 6$
$(D)^6C_3 – 4$
I know that the no. of ways in which I can make triangles from these lines is 6C3 since their are six lines and I will have to use 3 lines at a time. But, I will have to minus the cases were the chosen segments will just result in a straight line and not a triangle. How can I do that?