ID Great Britain Plate Please

I've started transferring my Great Britain from my ancient 1945 album
to a new one I just purchased. Of course, I have to check them more
closely and this one has me a little stumped. It is an 1876-81(?)
variety that I believe is Scott A30. I have checked the watermark, and
it is clearly Wmk 30 (Imperial Crown). Therefore, I thought it was
Scott 82 (1881). However, the plate number is hard to read and ends
in an "8". I think it may even be "28". My Scott catalog only lists
plate numbers 21, 22, and 23 for this item. Which is this? Thanks

It is plate #23. The cancellation just happens to obscure the relatively small openings in both 3's.

Good find! Thanks.