Let \( A = \{1, 2, 3, \ldots, 10\} \) and \( B = \left\{ \dfrac{m}{n} : m, n \in A,\, m < n \text{ and } \gcd(m,n) = 1 \right\}. \) Then \( n(B) \) is equal to:
\( 29 \)
\( 37 \)
\( 36 \)
\( 31 \)