Rashi on Terumah 27:14

English: עמדיהם שלשה THEIR COLUMNS THREE — There were five cubits space between one column and another column: between the column at the end of the southern row, standing at the southeast corner, to the first column which was one of the three in the east there were five cubits; from that to the second, five cubits, and from the second to the third, five cubits. It was similar at the other side of the entrance. And four columns for the screen are mentioned here, so that you have ten columns for the east corresponding to the ten columns in the west side (v. 12).