That's realy great . The exercice is to making box without ruler to practice fluidity in lines ! I deceided myself as a beeginer to post before ending exercices to avoid bing missing ! You do good job but not enought looking instructions or looking exemples .The real goal is not to make boxes than to inner boxes in ourselfs .Sorry for my english i am french .To draw boxes in the future in our drawing fluetly : Like chairs houses or every things looks like boxes in every contexts !