The diameter is 8cm
Explanation:Given the following:
[tex]\begin{gathered} \theta=104^o \\ \\ \text{Area(}A)=\pi r^2=56cm^2 \\ \text{Diameter(D)}=2r=\text{?} \end{gathered}[/tex]From the area of the circle, we can have the value for the radius, r as follows:
[tex]\begin{gathered} \pi r^2=56 \\ r^2=\frac{56}{\pi} \\ \\ r=\sqrt[]{\frac{56}{\pi}}\approx4cm \end{gathered}[/tex]We can now obtain the diameter by multiplying the radius by 2
[tex]D=2r=2\times4=8cm[/tex]