The formula for the circumference of a circle is 2*r*pi, where r is radius, and r=d/2.
If d = 6cm, then r = d/2 = 3 cm, and the circumference is 2*r*pi = 6*pi
If d = 12cm, then r = d/2 = 6 cm, and the circumference is 2*r*pi = 12*pi
12*pi/6*pi = 2
The circumference will be B)multiplied by 2.