63 is 90% of what number

Kayla has a $500 budget for the school party.she paid $150 for the decorations.food will cost $5.50 per student. what inequality represents the number of students,s, that can attend the party?

What is the simplified form of (3.25x10^3)(7.8x10^6) written in scientific notation?

X/y + 4y/x divided by x/y - 2y/x explain as in depth as you can how you simplfied the fractions. i don't know where to start on this : /