If n(A ∩ B′) = 9,

$\left.\begin{array}{rl}n\left(A \cap B^{\prime}\right) & =9 \\ \text { If } n\left(A^{\prime} \cap B\right) & =10 \\ n(A \cup B) & =24\end{array}\right\}$ given

n(A) = n(A ⋃ B) − n(A' ∩ B) 

n(B) = n(A ⋃ B) − n(A ∩ B')

i.e  n(A) = 24 − 10 =14

$n(B)=24-9=15$

$\therefore n(A \times B)=n(A) \cdot n(B)$

n(A × B) = 14 × 15 = 210