Given the linear programming problem:

Maximize $Z=3x_1+5x_2$

Subject $to$: $x_{1}4$

$x_{2}6$

$3x_1+2x_{2}18$

and $x_1,x_{2}0$

Discuss the effect on the optimality of the solution, when the objective function is changed to $3x_1+x_2.$