Harvey has 112 marbles and 7 trays that hold an equal number of marbles each. To find the number of marbles in 3 trays, you need to find the number of marbles that each tray holds. In order to do this, you need to divide:
112/7 = 16
(number of marbles divided by the number of trays)
This gives you 16, which is the number of marbles in 1 tray. To find the number of marbles in 3 trays, you need to multiply the number of marbles in each tray times the number of trays:
16 x 3 = 48
So, Harvey will display 48 marbles on 3 trays.