If you look at the first column, x + y + z add up to give a units digit z. If you look at the remaining columns, x + y + z add up to give a units digit x.
Here, the tens digit for the first column is added to all the remaining columns as the units digit remains the same. Thus, the tens digit turns out be y in the fifth column.
Now, to make an equation out of this: 1st column: x + y + z = 10y + z -> x = 9y 2nd column: x + y + z + y = 10y + x -> z = 8y Now, y here has to be 1 because if it's more than 1 then x,z > 10. Thus, the answer is z = 8.