数字与计量单位的表达 — 英语阅读题

阅读短文，回答问题。 Sam's Day at the Science Museum Last Saturday, Sam visited a science museum with his class. First, they watched a short film about the sun. The film was twenty minutes long. Then Sam looked at a big old clock in the hall. It took Sam fifteen minutes to walk around the whole museum. After lunch, Sam and his friend Ben ran a small race in the garden. Sam ran fifty metres, and it took him ten seconds. Sam said, 'What a fun day! We stayed at the museum for two hours.' Question: How long was the film? And how long did Sam stay at the museum?