No, because she will go over by .57 cents. So she won't be able to buy the gift. You can find the answer by dividing 18 by 7 and adding that answer to 18 to get the amount total you owe including tax.
You are not giving enough information but in one of the calsses the average of student's height might be greater than the other class beacause one of the two classes needs to have 1 extra person than the other calss
Let 6 cans represent an "order" of fruit juice. 72 cans means 12 orders (72 divided by 6). Since each order costs $2.50, 12 orders costs $30 (12 multiplied by 2.5).