Using Pythagoras theorem,
hypotenuse, h = radius
base, b = chord length/2
perpendicular, p = distance of chord from the center
formula used h^2 = p^2 + b^2 (Pythagoras theorem)
12^2 = p^2 + (14/2)^2
or 144 = p^2 + 49
or p = √95 cm
So the distance of chord from center is √95 cm
b) 12^2 = p^2 + (20/2)^2
or 144 = p^2 +100
or p^2 = 44
or p = √44
So the distance of chord from center is √44 cm