Element X decays radioactively with a half life of 15 minutes. If there are 340 grams of Element X, how long, to the nearest tenth of a minute, would it take the element to decay to 6 grams?

Each month, a shopkeeper spends 5x + 14 dollars on rent and electricity. if he spends 3x−5 dollars on rent, how much does he spend on electricity? for which value(s) of x is the amount the shopkeeper spends on electricity less than $100? explain how you found the value(s).