Suppose that you are solving a mixed$-$integer $($linesr$)$ program $($MIP$)$ with integer variables $x_1$ and $x_2,$ binary variable $x_3,$ and continuous variable $x_4.$ Your current branch$-$and$-$bound search tree is given below.

$($a$)$ Is this a minirsization or a maximization problem? How can you tell?

$1$

$($b$)$ What is the current best housd, the current incumbent objective function value, and the current optinulity gap?

$($c$)$ Which $($if any$)$ of Nodes A$,$ B$,$ C$,$ or D should be fathomed? Explain your reasoning,

$($d$)$ If you vere solving this MrI, what would your nest step be$?$