What is the current optimal solution? What is the current optimal objective value?

$(2)$ What is the new optimal objective value $($z$)$ if the right$-$hand$-$side coefficient of the first

constraint $($b$1)$ changes to $35?$

$(3)$ What is the new optimal objective value $($z$)$ if the right$-$hand$-$side coefficient of the second

constraint $($b$2)$ changes to $28?$

$(4)$ For what range of the objective coefficient of X$1($c$1)$ does the current optimal solution

remain optimal?

$(5)$ If the objective coefficient of X$2($c$2)$ changes to $0\mathrm{.}75,$ find the new optimal solution $($x$1,$ x$2)$

and the new optimal objective value $($z$).$