I know I'm supposed to do a factorial, but I dont know how to, my teacher just expects me to know how to.

William alston's gross weekly salary is $315. his weekly federal withholding is $35. the social security tax is 6.2% of the first $97,500 earned. the medicare tax is 1.45% of gross pay. the state income tax is 1.5% of gross pay. each week hey pays $8.40 for medical insurance. how much is deducted fro william's weekly wages for state income tax and medicare tax combined? for this problem, william has no exemptions.