I am really bad at geometry

Which math sentence can be used to determine if the triangle is a right triangle?

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).

Adele is five years older than timothy. in three years, timothy will be 2/3 of adele’s age. what is adele‘s current age?