Three tubes of brand A toothpaste cost $12,five tubes of brand B toothpaste cost $25,and eight tubes of brand C toothpaste cost $32 . Is the relationship between the number of tubes of toothpaste and the cost a proportional relationship? If it is, give the constant of proportionality assuming that cost depends on the number of tubes bought.
A. The relationship is proportional.The constant of proportionality is $4 per tube.
B.The relationship is proportional. The constant of proportionality is $5 per tube.
C. The relationship is proportional . The constant of proportionality is $12 per tube.
D. The relationship is not proportional.