Știm că: [tex]\text{card}(A \times B) = \text{card}(A) \cdot \text{card}(B)[/tex].=
[tex]\text{card}(A \times B) = 7 \cdot 11 = 11 \cdot 7.\\\text{Daca $\text{card}(B) = 11$} \implies 11 \vert 91 \text{, ceea ce e fals, deci $\text{card}(A) = 11$}\\\text{card}(C) = \frac{143}{\text{card}(A)} = \frac{143}{11} = \boxed{13}[/tex]
