The overlapping area is 3/5 of that of large greeting cards and 3/4 of that of small greeting cards.

So it can be seen that there are 9 copies of the two cards, and 3 copies of each card are used for overlapping, so the non-overlapping part is 3/9.

So the total area is: 270 ÷ (3/9) = 8 10.

Therefore, the area of overlapping parts without overlapping is: 8 10-270 = 540.

Overlapping area: 540 ÷ 2 = 270.