In this task, you're given a statement, 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'.

Context: This vicious act undermined Della Torre's grab on Milan, aggravated by Pope Gregory X, a Visconti of Piacenza, who in 1273 confirmed Ottone Visconti as legal Archbishop of Milan. Link Information: was Pope from 1 September 1271 to his death in 1276 Question: How long had Gregory X been Pope when he confirmed Visconti's appointment as Archbishop of Milan?
Answer: 2