The radii of the circle increases by 7.5 cm each ring: 7.5 cm, 15.0 cm, 22.5 cm, and 30.0 cm.
The area if the red target is the area of the largest circle minus the second to the largest circle plus the area of the third largest circle minus the area of the smaller circle
A=pi(30.0)^2 - pi(22.5)^2 + pi(15.0)^2- pi(7.5)^2
A=900pi-506.25pi+225pi-56.25pi
A=562.5pi is approximately 1767 cm^2