You would put this into a fraction
so for the salad

and for the fruit

cross multiply and
1. salad: 20% = 115 students
2. Fruit: 24% = 138 students
The answer is x=1
x^5=1
x=5[square]1
x=1
The correct answer is 45+45(0.15). This is because you need to first count the price, and then add on the tip which is a certain percentage of that price. Hope this helped!