The answer would be C What I did is converted 3 1/2 feet to inches. Since I know that 1 foot is equivalent to 12 inches I multiplied 3*12 (36) and I also know that half of a foot is 6 inches, so I added 6+36 (42). the question said that it could only fit LESS than 3 1/2 feet (42in.) So It has to be 41 inches or bellow. The answer choice C is the only one that meets these standards. I hope this helped ^^
only C will fit through the door because 42 inches is equal to 3 1/2 feet, you need to have a box with side lenghths less than 42 inches, the only one with all side lenghths less than 42 is box C
