Answer:
[tex]18*30+20*15=n[/tex]
Step-by-step explanation:
Represent the number of bagels all 18 large trays hold as [tex]18*30[/tex]. Represent the number of bagels all 20 small trays hold as [tex]20*15[/tex] (I suppose each small tray holds 15 bagels?). Add both expressions up and you get:
[tex]18*30+20*15=n[/tex]