In Argentina, the grading system for homework is as follows:

9-10 = Excellent (Excelente)
8 = Very good (Muy bueno)
7 = Good (Bueno)
6 = Sufficient (Suficiente)
5 = Insufficient (Insuficiente)
HB stands for "Hecho con buena voluntad", which means "Done with good will". E stands for "Esperado", which means "Expected". So, "Nota del trab.: HB, E" means that the homework was done with good will and was expected.

Спасибо!