Which situation is NOT a linear function?

An 18% discount on a watch saved a shopper $72. find the price of the watch before the discount

If you eat 4 medium strawberries, you get 48% of your daily recommenced amount of vitamin c. what fraction of your daily amount of vitamin c do you still need?

Shannon mary and john earn a weekly allowance ahannon earns the amount that is 2/3 of what john earns mary earns an amount that is 1 2/3 of what johns earns 20 dollars a week who eaens the greatest allowance and who earns the least