What is the simple interest on a loan of $310 for 4 months at 12% per year ?

Pls! does anybody know a shortcut for answering these types of questions in the future?

Jimmy can run 3.5 miles in 20 minutes. how far can ne run in one hour and ten minutes?

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.