If you need to know the lowest Or. No used in a pad (you didn't ask for it in your narrative but did in your sample file) you may need a tweak to the formula I gave for that to:
=MINIFS(Table1[OR No.],Table1[OR No.],">=" & FLOOR(Table1[@[OR No.]]-0.1,50))
this is to cater for when the Or. No. was an exact multiple of 50.