Area of sheet of board = 39 × 52 = 2028
Area of a single pad = 6 × 12 = 72
Number of pads you would get out of a sheet = 2028 ÷ 72
= 28.1666...
0.1666... of a pad is not a whole pad so it can be ignored;
You would get 28 pads from one sheet of board.