A tip of $5 for a bill of $40 represents what percent of the total bill

Which is an equation for the nth terms of the sequence 12,15,18,21

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).

3382-299=3383- ? fill in the blank?