Question $8$

Keeping $c_1$ constant at $c_1=15,$ the interval for the net change in

$c_2,$ represented by $c_2,$ while the current optimal solution

remains optimal is

$-\frac{7}{6}{c}_2\frac{2}{9}$

$-\frac{9}{2}{c}_2\frac{6}{7}$

$-\frac{2}{9}{c}_2\frac{7}{6}$

$-\frac{6}{7}{c}_2\frac{9}{2}$