Question 81958
Let x be the unknown number. Then the sum of it and -16 is represented by:
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x + (-16) 
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And the problem tells you that this is to equal 3. In equation form this can be written as:
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x + (-16) = 3
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Since the parentheses are preceded by a plus sign, they can be removed without changing
the sign of the term inside the parentheses.  When you do that removal, the equation 
becomes: 
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x - 16 = 3
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to solve for x get rid of the -16 on the left side by adding 16 to both sides. The addition
of 16 to both sides results in:
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x - 16 + 16 = 3 + 16
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On the left side the -16 and + 16 cancel each other out. And on the right side the 
3 + 16 is 19. So the equation becomes:
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x = 19
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The missing number that solves this problem is +19
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Hope this helps you to understand the basics of this problem and shows you a way to logically
solve it.