Which of the following is the length of the radius of circle A?

Answer:
Radius=9
More Specific: 8.94427191
Step-by-step explanation:
a^2+b^2=c^2
a is the radius of circle A
b is 8
c is 12
a^2+8^2=12^2
Simplify
a^2+64=144
Move 64 to the other side
a^2=80
a=8.94427191
or 9