Purchasing something you don’t need means?

Which expressions are equivalent to k/2 choose 2 answers: a k-2 b 2/k c 1/2k d k/2 e k+k

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

Which of the following would be a good name for the function that takes the weight of a box and returns the energy needed to lift it?