A sandwich store charges $20 to have 3 turkey subs delivered and $26 to have 4 delivered. Is the relationship between number of turkey subs delivered and the amount charged proportional? I know the answer is no but I need help with understanding how the answer is no, please explain!

According to a study conducted in 2015, 18% of shoppers said that they prefer to buy generic instead of name-brand products. suppose that in a recent sample of 1500 shoppers, 315 stated that they prefer to buy generic instead of name-brand products. at a 5% significance level, can you conclude that the proportion of all shoppers who currently prefer to buy generic instead of name-brand products is higher than .18? use both the p-value and the critical-value approaches.