I need help quick on this question too don't give wrong answer and explain

Determine the fraction of total interest owed. after the fourth month of a 12-month loan: the numerator is: {(n + ) + (n + ) + (n + ) + (n + )} = , and the denominator is: {(n) + (n + 1) + + (n + )} = . therefore, the fraction is numerator/denominator (to the nearest tenth) =

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

Ineed with number 6 , explain how to get 1978