direct addition and subtraction

1+5+2+1-3

• 6

• 0

• 8

• 9

3+1+5-8+2+1-4+6

5+3+1-6+1+5-4+3

1+5-6+4-2+5-7+2

• 4

• 0

• 7

• 2

3+6-4+2+1-6+2+5

• 6

• 9

• 3

• 1