Answer:
1. What number plus 9 equals 18
Explanation:
Let's write each question as an algebraic equation.
1: What number plus 9 equals 18? 
 
2: What number minus 18 equals 9? 
 
3: What number is 9 more than 18? 
 
4: What number plus 18 equals 9? 

Therefore, the answer is What number plus 9 equals 18.
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