Answer:
1)
An onto function is a function where it's range is the term in that function.
[tex]{ \sf{if \: function \: is \: x \: to \: y}} \\ { \sf{then \: range \: of \: function \: is \: y}} \\ i.e \: \: f(x) = y[/tex]
It is given by formula:
[tex]{ \boxed{ \sf{ {x}^{y} - {}^{x} c _{1}(n - 1) {}^{y} + {}^{x} c _{2} (x - 2) {}^{y} + ..... {x}^{n} }}}[/tex]
2).
[tex]f(k) = 2k - 1 \\ but \: f(k) = 5 \\ 2k - 1 = 5 \\ 2k = 1 + 5 \\ 2k = 6 \\ k = 3[/tex]
