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.