Data:
x: number of persons
Delivery fee: $14
Additional: $5.25x
Spend no more than $350 (the final cost needs to be less than or equal to 350)
Final cost: y
You have the next:

Use the last inequality to find the number of persons x:
To solve for x:
1.Substract 14 in both sides of the inequality:

2.Divide into 5.25 both sides of the inequality:

Then, the number of persons need to be less than or equal to 64. (Can be invited 64 or 47)