then comes the tens-column. the tens-column might contain two digits: the tens-digit of the first number and the tens-digit of the second number. if one of the numbers has a missing tens-digit then the tens-digit for this number can be considered to be a 0. add the tens-digits of the two numbers. then, if there is a carry digit, add it to this sum. if the sum was 18 then adding the carry digit to it will yield 19. if the sum of the tens-digits (plus carry digit, if there is one) is less than ten then write it in the tens-column under the line. if the sum has two digits then write its last digit in the tens-column under the line, and carry its first digit (which should be a 1) over to the next column: in this case the hundreds-column.