"Hello and thank you, teacher."
Translation:Halò agus tapadh leibh a thidseir.
It's to do with formality. "leat" is used when speaking to a child or a peer, while "leibh" is when talking to someone older or more senior than you as well as when talking to more than one person. I regard it similar to the German uses of "du" vs "sie". As a general rule, if you'd use "du" in German, then use "leat" in Gaelic; likewise use "leibh" where you'd use "sie".