We first calculate the area of the whole circle the formula for the area of a circle is
[tex]A=\pi r^2[/tex]r is the radius in this case r=5
we substitute the value
[tex]A=\pi5^2=25\pi[/tex]then we divide 120 between 360 in order to find the ratio of the shaded area
[tex]\frac{120}{360}=\frac{1}{3}[/tex]we multiply the number above by the area of the whole circle to obtain the shaded area,
[tex]SA=25\pi\cdot\frac{1}{3}=\frac{25\pi}{3}[/tex]