Even more fun with matrices; How is this even possible?!?

My Solutic

Near the end of class, we talked about use of a colon $($ : $)$ to both create, and index from, matrices. In this problem set, you'll be tasked with both uses of the colon.

Starting with the matrix here:

$A=\left[\begin{array}{ccccc}7& 8& 9& 4& 3\\ 9& 10& 2& 1& -1\\ 4& 8& 3& 0& 5\\ 5& 3& 9& -2& 0\end{array}\right]$

Write the command, or commands, to select the second column from A and save this into an matrix called $B.$

Write the command, or commands, to select the third row from A and save this into an matrix called $C.$

Write the command$($s$)$ to make an identical matrix to A except change the $3$ rd row, $4$ th column to $-75,$ and save this into an matrix called $D.$

Write the command$($s$)$ to make a matrix which replaces the first column of $D$ with the column vector $C{V}_{\text{n}\text{e}\text{w}}$ and assign to a matrix called $E.$

$C{V}_{\text{n}\text{e}\text{w}}=\left[\begin{array}{c}20\\ 30\\ 40\\ 50\end{array}\right]$

Write the command$($s$)$ to make a matrix which replaces the last row of $E$ with a row vector that starts with $80$ and counts down in steps of $20$ ; assign to $F.($hintl use $$