Why is the gcf of two numbers is sometimes one

Write a story that matches with the expression 42x-5 pls hurry

Pls brainliest will be awarded if answer is correct

Kayla made observations about the sellin price of a new brand of coffee that sold in the three different sized bags she recorded those observations in the following table 6 is $2.10 8 is $2.80 and 16 is to $5.60 use the relationship to predict the cost of a 20oz bag of coffee.