Explain my answer i put in isnt correct plz explain

What number produces an irrational number when multiplied by -1.25

Oscar and julie ashton are celebrating their 15th anniversary by having a reception hall. they have budgeted $4,500 for their reception. if the reception hall charges a $90 cleanup fee plus & 36 per person, find the greatest number of people that they may invite and still stay within their budget.

Ineed in figuring out this problem.