Don't shout it or they'll all want one

Level pending

Zaphod is collecting figurines from cereal packets. Each packet of Space Crunchers contains one of 4 different models, each equally likely. Zaphod hates cereal, but loves himself, so keeps buying Space Crunch until he has all four models. What's the expected number of packets Zaphod consumes?

Give your answer to two decimal places.

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