A) the geneal formula to find the sum of a figure is:
[tex](n-2)\cdot180[/tex]where n is the number of sides, so for a 13-gon will be:
[tex](13-2)\cdot180=11\cdot180=1980[/tex]B) The sum of the angles is 720 so we can replace that in the general formula so:
[tex](n-2)\cdot180=720[/tex]so we can solve for n to find the number of sides:
[tex]\begin{gathered} (n-2)=\frac{720}{180} \\ n=4+2 \\ n=6 \end{gathered}[/tex]