13. (5 points)
The distance from Earth to Planet Sadala is 80 light years (Note: A light year is a unit of length). Vegeta and Goku depart from Earth to Planet Sadala. Vegeta departs 1 day earlier than Goku. If Vegeta and Goku fly in a straight line, they can both fly 10 light years per day. How many days after Goku's departure will Vegeta be exactly in the middle of Goku and Planet Sadala?
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