6.99 $ + 0.55 $ = ??? pls help (ノ _ <、)

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).

Icould really use some with this question.

Wich statement could be used to explain why the function h(x)= x^3 has an inverse relation that is also a function