When we are writing number sentences from any word problems we need to use the math language in the word problem to help us. In order to solve number sentences to find a missing number, it helps to use the opposite operation to do so.
Have a look at this video where I explain this in more detail.
Example Questions:
question 1
When I add $6$6 to the number $\editable{?}$?, the answer is $13$13.
Fill in the empty spaces below to match the sentence.
$\editable{?}$?$+$+$\editable{}$ $=$= $\editable{}$
What is the missing number?
$\editable{}+6=13$+6=13
question 2
When I subtract $7$7 from a number (?), the answer is $12$12.
Fill in the spaces below to match the sentence.
$\editable{?}$?$-$−$\editable{}$ $=$= $\editable{}$
What is the missing number?
$\editable{}-7=12$−7=12
question 3
When a number is added to $24$24 the answer is the same as $64$64 minus $14$14.
What is the number?