What is the best way to: How do I cut off the top of the box ?

Available options:
[I] Draw with a pencil a line parallel to the top of the box and 3 inches lower than the top of the box. Then, cut on the line with a band saw..
[II] Draw with a pencil a line parallel to the top of the box and 3 inches lower than the top of the box. Then, cut on the line with a belt sander..
Answer:
[I]