Question: How long was the rule of the dynasty that was active when the Rosetta Stone was inscribed?

Related documents: [0]  [DOC] The Ptolemaic dynasty (Ancient Greek: Πτολεμαῖοι , "Ptolemaioi"), sometimes also known as the Lagids or Lagidae (Ancient Greek: Λαγίδαι , "Lagidai", after Lagus, Ptolemy I's father), was a Macedonian Greek royal family, which ruled the Ptolemaic Kingdom in Egypt during the Hellenistic period. Their rule lasted for 275 years, from 305 to 30 BC. They were the last dynasty of ancient Egypt. [END] 
[1]  [DOC] The Rosetta Stone is a granodiorite stele, found in 1799, inscribed with three versions of a decree issued at Memphis, Egypt in 196 BC during the Ptolemaic dynasty on behalf of King Ptolemy V. The top and middle texts are in Ancient Egyptian using hieroglyphic script and Demotic script, respectively, while the bottom is in Ancient Greek. As the decree has only minor differences between the three versions, the Rosetta Stone proved to be the key to deciphering Egyptian hieroglyphs. [END]  
Answer: 275 years
275 years