Answer: one minute, forty-five seconds(1:45secs)
Explanation: DRO (DIFFERENTIAL REINFORCEMENT OF OTHER BEHAVIOR) is a procedure used to reinforce or reward a student of an undesireable or negative Behavior was not repeated over a given period of time. This approach is positive and not Purnishment or penalty is involved in this procedure, in certain instances it requires a 1:1 Student: Teacher ratio and an observer who is independent to record data and where necessary, It usually doesn't put the students under any pressure or compulsion.