We know that the sum of each line is same in a magic square.
Sum of the first column is 4 + 3 + 8 = 15
So the magic number here is 15.
The misisng number in second column is 15 - (5 + 1) = 15 - 6 = 9
The misisng number in last column is 15 - (2 + 7) = 15 - 9 = 6