Operant conditioning is used by Mark .
The instrumental conditioning is the other name given for operant conditioning. It can be considered as a method of learning in which rewards and punishments are used for modification of certain behaviors. This forms a relativity between certain behavior and the consequences of that behavior.
In the example given, Mark has decided to give rewards in order to make his employees to reach office at time. Monthly rewards are given to those employees who did not take breaks and thus he is using the principle of Operant conditioning .