Complex sentence: The latter agreed to conquer Sicily, with the promise to leave it to Euphemius in exchange for a yearly tribute, and entrusted its conquest to the 70 year old "qadi" Asad ibn al-Furat.
Split into simpler sentences: The latter agreed to conquer Sicily, with the promise to leave it to Euphemius in exchange for a yearly tribute. He entrusted its conquest to the 70 year-old "qadi", Asad ibn al-Furat.