'Explain how an act utilitarian would make a moral decision'

Act utilitarians assert that, when making morally relevant choices, on a case-by-case basis, consequences ought to be the only frame of reference for a moral agency. Thus, they uphold the primacy of the Utility Principle, that utility and thus pleasure ought to be maximised for the greatest number of moral patients. Indeed, Bentham theorised a mathematical formula, the Hedonistic Calclus, which enables agents to work out a course of action based upon its purity, duration, extent, fecundity, propinquity, and certainty with reference ot utility. Thus, if an act utilitarian was faced with a choice to allow a hurtling trolley to continue down a street and kill five, or to pull a lever to change its course and kill two, they would pull the lever. Killing two is three less dead, so it would produce the greatest utility and thus pleasure. Hence, act utilitarians ultimately make moral decisons based upon the predicted utility and thus pleasure the decision will create.