6. [3 mark] State whether or not the following functions have a well-defined inverse. If the inverse is well-defined, define it. If it is not well-defined, provide justification. \begin{array}{l} \text

{ (a) } f: z \rightarrow z_{1} f(x)=7 x-7 \\ \text { (a) } f: \mathbf{R} \rightarrow \mathbf{R} \text { . } f(x)=7 x-7 \end{array} (c) A = {a, b, c, d,e}. f: P(A) → {0,1,2, 3, 4,5}. f(2) = |2|. It maps a set to the number of elements it contains.