Solution 0.4.8.1.

\(f(\{1,2,3\}) = \{a,b\}\) since \(a\) and \(b\) are the elements in the codomain to which \(f\) sends \(1\text{,}\) \(2\text{,}\) and \(3\text{.}\)

\(f\inv(\{a,b\}) = \{1,2,3,4,5\}\) since these are exactly the elements that \(f\) sends to \(a\) and \(b\text{.}\)

\(f\inv(d) = \emptyset\) since \(d\) is not in the range of \(f\text{.}\)