Answer:
y=15x+250 (x is the number of guests)
Step-by-step explanation:
the 15 is the slope, so that is the number that has to be multiplied by. The 250 is an additional fee that doesn't change, so it's just added on.
You can do 5+5+10, 6+6+8, 9+9+2, 4+4+12, 3+3+14, 2+2+16, 1+1+18. I believe these are all of them, so there are 7 ways.