In a typical jury trial, whose duty is it to interpret the law? the judge the jury the prosecutor the witnesses

Horton automatics and the industrial division of the communications workers of america, the union that represented horton’s workers, negotiated a collective bargaining agreement. if an employee’s discharge for a workplace-rule violation was submitted to arbitration, the agreement limited the arbitrator to determining whether the rule was reasonable and whether the employee had violated it. when horton discharged employee ruben de la garza, the union appealed to arbitration. the arbitrator found that de la garza had violated a reasonable safety rule, but “was not totally convinced” that horton should have treated the violation more seriously than other rule violations. the arbitrator ordered de la garza reinstated. can a court set aside this order