8.4. A rectangular table has 6 rows and 7 columns and includes 42 squares of size $1 \times 1$. In each square, one of the numbers 0 or 1 is written such that for any two different rows, the sums of the numbers written on them are different, and for any two columns, the sums of the numbers written on them are equal. Find the sum of the numbers written in the first column.