I believe the answer is 9, because 1/3 is .33 so 33%. so 33% is equal to 3 buttons and add another 66% which would be another 6 buttons would add up to 99% in all. after that I don't think they would add a quarter of a button.
The answer would be 9 I'm not exactly sure how to explain it correctly but the way it did it was I multiplied the 3 in the 1/3 by the 3 buttons and it was 9 sorry hope it helped
The volume of rectangular prism = length x height x width so sub in the above equation we get 840 = length x 6 x 10 length = 840 /(60 x 10) length = 14 inches
