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Here is the full answer:

$\begin{align*} \dbinom{15}{2} &= \dfrac{15!}{13!2!} \\ &= \dfrac{15\times 14}{2\times 1} \\ &= 15 \times \dfrac{14}{2} \\ &= 15 \times 7 \\ &= \boxed{105}. \end{align*}$

15nCr2 =105

Very nice, Mr. O   !!!!!!