The length of the box is 3 x the height of 12 inches = <<3*12=36>>36 inches.
The width of the box is 36 inches / 4 = <<36/4=9>>9 inches.
The volume of the box is the height of 12 inches x the length of 36 inches x the width of 9 inches = <<12*36*9=3888>>3,888 cubic inches.
#### 3,888