[tex]1hr=60mins[/tex]
[tex]60x3mins[/tex]
Basically meaning in 20 hours time but then we need include the full hour.
[tex]60x20=1200mins[/tex]
[tex]3x20=60mins[/tex]
[tex]1200+60=1260[/tex]
Conversion: [tex] \frac{1260}{60} =21hr[/tex]
[tex]6pm[/tex] on saturday + [tex]21hr=3pm[/tex] on sunday
Hope this helps