For this case we have to:
There are 6 plants per tray.
There are 6 trays for each flat, so for each flat there are [tex]6 * 6 = 36[/tex] plants.
Saturday day:[tex]18 flat * 36 plants = 648[/tex]
Thus, on Saturday they sold 648 plants.
Sunday: [tex]21 flat * 36plants = 756[/tex]
Thus, on Saturday they sold 756 plants.
Thus, in total [tex]648 +756 = 1404[/tex]plants were sold.
Answer:
[tex]648 +756 = 1404[/tex] plants were sold.