Answer:
Explanation:
C = πd is in the category "direct variation." If d increases, C increases also.
Initial diameter: 5 cm; C = 5π cm;
Final diameter: 15 cm (which is 3 times 5 cm)
So, multiplying the initial diameter (5 cm) by 3 to obtain 15 cm, results in the initial circumference being multiplied by 3; from 5π cm the circumference becomes 3(5π cm), or 15π cm.