Post haec:
"These things" being the fact that the forces of the Marian factor had been stopped in Africa and Sulla was now unopposed.
de Mithridate ... triumphavit:
Translate "He celebrated a triumph ... concerning Mithridates."
Cn. etiam Pomeius:
Eutropius is delaying the etiam and placing it between the praenomen
and cognomen.
de Africa triumphavit:
See note above on de Mithirdate ... triumphavit.
quod ... tributum erat.... triumphavit:Quod is acting as a relative pronoun, though
the antecedent is a little unclear. Translate as "he celebrated a triumph, which had been offered..."
annum agens:
This form of ago should be translated as "living." Take note that when
Pompey was "living his twenty-fourth year of life,"
he was twenty three years old. Eutropius is again stressing how young Pompey is at this time.