Question

If the diameter of a circle changes from 5 cm to 15 cm, how will the circumference change

Answer 1

its 3
5 times 3 = 15 so your answer will be 3

Answer 2

we know that
[circumference]=2*pi*r

for diameter=5 cm
r=5/2----> r=2.5 cm
[circumference]=2*pi*2.5-----> 5*pi cm

for diameter=15cm
r=15/2----> r=7.5 cm
[circumference]=2*pi*7.5-----> 15*pi cm

the answer is
the circumference will be three times higher