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Here's a table that can from the problem.

Inventory of Clocks and Frequency of Chimes

Types A has 10 clocks. Chimes n times on the nth hour. Chimes once on the half hour.

Type B has 5 clocks. Chimes n times on the nth hour.

Type C has 3 clocks. Chimes once on the hour. Chimes once on the half hour.

The question:

A merchant sells three types of clocks that chime as indicated by the table above. What is the total number of chimes of the inventory of clocks in the 90-minute period from 7:15-8:45?