At the livestock market, the sheep were secured in 36 pens arranged in a 6x6 grid, the number in each pen shown below.

7 5 5 3 6 2
8 1 7 6 5 1
5 8 4 3 4 5
4 6 8 1 2 9
1 2 8 4 7 8
6 5 3 7 4 5

"I want to make a tidy sum out of it," said the farmer. So, in line with the farmer's wishes, the buyer bought all of the sheep in each of 12 pens.

Remove 12 of the 36 numbers to leave four numbers in each row and column, so that each of the six horizontal lines and each of the six vertical lines totals 20.