A two variable linear program has the following characteristics: The objective function maximizes $7$X$1+12$X$2$;Constraint $1$ states that X$11$; constraint $2$ states that X$21$; constraint $3$ states that X$10$; constraint $4$ states that X$2$ z O$.$ Which of the following statements is true about the linear program? In the optimal solution, constraint $1$ has a slack of zero and constraint $2$ has a surplus of $1.$ In the optimal solution, constraint $3$ has a slack of $0.$ In the optimal solution, constraint $1$ has "slack variable" $=0.$O The optimal solution value is $19\mathrm{.}75.$