Given the task definition and input, reply with output. In this task, you're given a passage, further information available on a particular linked term from the statement, and a question. Your job is to generate the answer to the question by using the information provided. If there is no clear answer obtainable, output 'none'.

Passage: He is the brother and usurper of Numitor and son of Procas. He was said to have reigned 42 years before his death (794-752 BC). His brother had been king, but Amulius overthrew him, killed his son, and took the throne. He forced Rhea Silvia, Numitor's daughter, to become a Vestal Virgin, a priestess of Vesta, so that she would never bear any sons that might overthrow him. However, she was raped or seduced by the god Mars, resulting in the birth of the twins. Rhea was thrown into prison and her sons ordered to be thrown into the river Tiber. The twins washed up onto dry land and were found by a she-wolf who suckled them. Later their mother was saved by the river god Tiberinus who ended up marrying her. Romulus and Remus went on to found Rome and overthrow Amulius, reinstating their grandfather Numitor as king of Alba Longa.
Link Information: none Question: How long had Numitor been king when his brother Amulius overthrew him?
Answer: none