How to plot the discrete time signal $u[2k - 3]$?
$u[n]$ is the unit step function with the definition
$$ u[n] = \begin{cases}{ 1 ~~~, ~~~n \geq 0 \\ 0 ~~~,~~~ n &lt; 0 } \end{cases} $$
Then you will have for $u[2k-3]$ as
$$ u[2k-3] = \begin{cases}{ 1 ~~~, ~~~ 2k-3 \geq 0 \\ 0 ~~~,~~~ 2k-3 &lt; 0 } \end{cases} $$
$$ u[2k-3] = \begin{cases}{ 1 ~~~, ~~~ k \geq 2 \\ 0 ~~~,~~~ k&lt; 2 } \end{cases} $$
I think this last line is easy to see. You can plot it wrt the variable $k$.