The answer is B. 9 because GJ is the circumference of the circle and they’re basically asking you to find the radius and the radius is half the circumference and half of 18 is 9 so the answer would be B.
Fractions need common denominator to add or subtract them because without denominators a fraction is not a fraction, it is a whole number Example - 2/8 is a fraction but 2 is not a fraction
