Mathematically, a line from the center of the circle to a chord divides the chord into 2 equal portions
From the first part of the question, we can get the radius of the circle
The radius form the hypotenuse, the two-portions of the chord (12/2 = 6 cm) and the distance from the center to the chord forms the other side of the triangle
Thus, by Pythagoras’ theorem; the square of the hypotenuse equals the sum of the squares of the two other sides
Thus,
r^2 = 8^2 + 6^2
r^2= 64 + 36
r^2 = 100
r = 10 cm
Now, we want to get a chord length which is 6 cm away from the circle center
let the half-portion that forms the right triangle be c