Which equation is equivalent to y/a=b

Need on this one asap im almost done with this subject

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).

What is the value of x in the following equation. -x ^3/2 = -27