I need help with this pls

If f(x)=3x+1 and f^-1=x-1/3, then f^-1(7)=

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).

Triangle knm is what is true about the sides of knm