Learn to copy and delete cells in one click
You can copy or duplicate a cell very easily by clicking on the cell in question. Once the blue border appears, select in the blue cell menu the icon to duplicate (double square shape). Duplicate as many times as necessary and remember that every time you copy a cell, its size will be the same as the original so bear in mind to add up and not got over 100%.
Likewise, to delete a cell you must select the cell in question and click on the trash can icon that appears in the blue menu right underneath the cell. Once you delete a cell, the row will be restructured and its size will add up to 100%.