What's the Missing Number?

What number goes in the box?
∎ + 5 = 13

• 8
• 18
• 5
• 13

What number goes in the box?
∎ - 5 = 13

• 8
• 18
• 5
• 13

What number goes in the box?
6 + ∎ = 18

• 24
• 12
• 18
• 6

What number goes in the box?
6 - ∎ = 4

• 2
• 10
• 4
• 6

What number goes in the box?
15 - ∎ = 7

• 15
• 7
• 8
• 22

What number goes in the box?
20 - ∎ = 7

• 13
• 27
• 20
• 7

What number goes in the box?
14 + 5 = ∎

• 19
• 9
• 14
• 18

What number goes in the box?
14 - 5 = ∎

• 19
• 9
• 14
• 18

What number goes in the box?
14 - 4 = ∎

• 10
• 18
• 14
• 1