Answer:
Half of cord 24/2 = 12
Step-by-step explanation:
In the circle with r = 13 we have 13^2 = 12^2 + a^2 where a = the distance from the centre of this circle to the cord. Thus a = 5. Then the distance from the cord to the other circle centre is 21 - 5 = 16. In the second circle you can write r2^2 = 16^2 + 12^2. The r2 = sqrt (400) = 20