the column sums (that is you add down the coulmns then accross the column
sums. But this is equal to the sum of the integers from 1 to 240, you are
supposed to know that the sum of the first n positive integers is
So in this case n=240, and s=120 241.
This should be equal to 15x, but as s is not divisible by 15 no such x exists as
an integer, so the task is impossible.