A quadrilateral is symmetric across one of its diagonals and can be inscribed in a circle. The measure of one of its interior angles is \( 80^{\circ} \). Determine the measure of its largest interior angle.
Which of the given numbers is the product of all the solutions of the following exponential equations?
\begin{align*} 3^x+3^{x+2}&=30\\ 3^{x+1}+3^{x-1}&=\frac{10}9 \end{align*}