Answer:
firms coordinate their decisions to act as a multi-plant monopoly..
Explanation:
A cartel is a group of countries or firms that have reached an agreement to work together in order to influence or decide market prices for goods and services by controlling sales and the level of production or quantity of output.
In the cartel model firms coordinate their decisions to act as a multi-plant monopoly, wherein the level of production or quantity of output is divided into many production plants.
The main purpose of having the cartels do this is to make marginal cost (MC) equal to marginal revenue (MR) in the various production plants, so as to create monopoly profits by making sure each plant has its own cost.