if the total cost is $500 that means that total percentage is 100%, she saves 25% that is $125, she needs additional 75% (where 100% - 25%), that means that she needs 75% 0f $500 which is $375 in order to have enough money to buy her tablet.
Its a trick question, 15% of 6th grade teachers give HW, but there are 12 teachers. its not gonna be 15% of 12, because you would also get a fraction of a teacher.