Help please 10 points!

Which of the fallowing best completes the sequence 12,8,5, a) 1 b) 2 c)4 d)0

Mary works for a company that ships packages and must measure the size of each box that needs to be shipped. mary measures a box and finds the length is 7 inches, the width is 14 inches, and the height is 15 inches. what is the volume of the box? [type your answer as a number.]

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?