Can you replace the question mark with a number?

A young woman, pursuing a graduate degree in art history, was going to Italy to study the country's greatest works of art.
Since there was no one to look after her grandmother while she was away, she took the old lady with her.
At the Sistine Chapel in the Vatican, she pointed to the painting on the ceiling. 'Grandma, it took Michelangelo a full four years to get that ceiling painted.'
'Oh my, 'the grandmother says.
'He and I must have the same landlord.'