Is it a prerequisite to employ means (such as working) for prayers for provision to be answered, or is the father's job and salary considered a sufficient means?

Allah is capable of providing for His servants with or without means. He has linked causes to their effects, as happened with Mary, peace be upon her, who received provision without means due to her devotion to worship, and with means by shaking the palm trunk to obtain fresh dates. Provision is in Allah's hand, and a person will only receive what has been decreed for them; their provision will come to them just as their appointed time of death will come. Among the causes of provision are supplication (dua), seeking forgiveness (istighfar), and obedience. Allah may test a believer to expiate their sins, elevate their status, and manifest levels of servitude within them. One must be patient and seek reward, for Allah is with the patient, and He does not let the reward of those who do good go to waste. Indeed, with hardship comes ease. Fearing Allah opens the doors of provision, and one must turn to Him with certainty, and beware of the whisperings of Satan. A person's provision may come from any direction, for Allah has guaranteed the provision of every creature and delivers it to them.