Express the set in interval notation 9

6n^2-7n-75=0 solve by quadratic formula

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).

How can you tell when x and y are not directly proportional?