The first addend is unchanged, and the second addend is divided into two parts. Part of it and the first addend form 10 (ten digits are written as 1), and the rest is one digit of the sum (written after 1).

9+7=( 16) 9+( 1+6)

8+4=( 12) 8+(2+2)

6+7=( 13) 6+(4+3)