Solve for the Unknown Number

6 + ? = 15

• 8

• 21

• 9

• 10

8 + ? = 16

• 7

• 10

• 9

• 8

3 + ? = 12

• 15

• 9

• 10

• 6

4 + ? = 12

• 8

• 16

• 4

• 10

15+__=21

• 7

• 6

• 8

10+_=15

• 9

• 1

• 5

• 8

Find the missing addend for this equation 
5+__= 8

• 3
• 6
• 5
• 8

Find the missing addend for this equation
__+ 6 = 10

• 9
• 4
• 2
• 6

Find the missing addend for this equation
4+__= 7

• 7
• 8
• 3
• 4

Find the missing addend for this equation
__+7= 8

• 1
• 8
• 7
• 3