Help please??!?? i don’t understand

If f(x)=3x+1 and f^-1=x-1/3, then f^-1(7)=

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.

In an equilateral triangle, each angle is represented by 5y+3. what is the value of y? a. 9.7 b. 10.8 c. 11.4 d. 7.2