How to determine relationship between two variables with standard deviation?

Given the equation f(x)=a(b)x where the initial value is 40 and the growth rate is 20% what is f(4)

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.

Divide. –4.2 ÷ 6 = a –0.7 b 0.7 c –7 d 7 me