Affiliation: | a Faculty of Mechanical Engineering, Dositejeva 19, 36 000 Kraljevo, Serbiab High School for Preschool Pedagogues Gnjilane, Kara?or?ev trg bb, 17 520 Bujanovac, Serbiac Faculty of Natural Sciences and Mathematics, Gazibaba bb, 1 000 Skopje, Macedoniad Faculty of Engineering, Knjaza Miloša 7, 38 220 Kosovska Mitrovica, Serbia |