From the exercise we know that there are 20 people, that 7 are men and 13 are women if only one is going to choose and one we must multiply their combinations
[tex]C_{m,n}=\frac{m!}{n!(m-n)!}[/tex]For males we have
[tex]\begin{gathered} m=7 \\ n=1 \\ C_{\text{male}}=\frac{7!}{1!(7-1)!} \\ C_{\text{male}}=7 \\ \end{gathered}[/tex]For females we have
[tex]\begin{gathered} m=13 \\ n=1 \\ C_{\text{female}}=\frac{13!}{1!(13-1)!} \\ C_{\text{female}}=13 \end{gathered}[/tex]Now we multiply the combinations to know how many options the director has to choose his actors
[tex]\begin{gathered} C_{\text{male}}\cdot C_{\text{female}}=7\cdot13 \\ C_{\text{male}}\cdot C_{\text{female}}=91 \end{gathered}[/tex]