Pls help me with this, thanks

For each proportion find the unknown number x 1/5/8=×/15

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.

Solve this system of equations. 12x − 18y = 27 4x − 6y = 10