Expository means elaborate. So think up of an idea on deterrence and just write about it.
To start of, deterrence implies doing something that makes some people not want to do an action. So, examples of deterrence are major consequences if one gets caught, or consequences of merely doing the act as well.
A possible deterrent policy would be something like a curfew at night to prevent juvenile delinquents from damaging property. That's the harm, the property damage. The solvency is by enacting the curfew, juvenile delinquents will be in trouble if they get caught at night and thrown in jail. The impacts will be that there will be fewer property damages at night, juveniles won't be loitering around at night and could be doing something better during the day.
So just talk about a bunch of similar policies. The "HARM - SOLVENCY - IMPACT" model of flowing I just used (which I regularly use in debate) is a good way to frame your ideas.