Consider this explanation:
1) for radius (r):
S=πr², where S - area, r - radius. ⇒ r=√(S/π)=√400=20 ft.;
2) for circumference (L):
L=2πr, where r- radius ⇒ L=2π*20=40π ft.;
3) for the diameter (D):
D=2r, where r - radius, ⇒ D=40 ft..
It's looking for the measures
m<F + m<G = 180°
(4x)° + (8x)° = 180°
12x = 180°
÷12 ÷12
x = 15
check your work
m<F + m<G = 180°
(4x)° + (8x)° = 180°
4(15)° + 8(15)° = 180°
60° + 120° = 180°
