Let $A= \{2, 3, 4, 5, ..., 17, 18\}$. Let '≈' be the equivalence relation on A × A, cartesian product of A with itself, defined by $(a, b) ≈ (c, d)$ if $ad = bc$. Then, the number of ordered pairs of the equivalence class of (3, 2) is _____.

The number of ordered pairs in the equivalence class of (3,2) is the number of ordered pairs (a, b) satisfying

$(a, b)≈ (3, 2)$ i.e. $2a = 3b$ i.e. $\frac{a}{b}=\frac{3}{2}$

Clearly, such ordered pairs are (3,2), (6, 4), (9, 6), (12, 8), (15, 10) and (18, 12).