Mind Your E's

A logical approach to this would be to first count all the E's that are already in the sentence which is 8. Then, you would need to find a word that matches the amount to E's in the sentence - while keeping in mind the number of E's in that word as well.

Ten has $1$ "E", If you add "ten" into the sentence (8+ 1 ) there would be 9 E's which is not ten .

Eleven has $3$ "E's", If you add "eleven" into the sentence (8+ 3 ) there would be 11 E's which is eleven .

Twelve has $2$ "E's", If you add "twelve" into the sentence (8+ 2 ) there would be 10 E's which is not twelve .

Thirteen also has $2$ "E's", If you add "thirteen" into the sentence (8+ 2 ) there would be 9 E's which is not thirteen .

So our final answer to this would be $\boxed{eleven}$ .

E's without the number name is 8 therefor eleven is the only solution. 8+3=11

There is no solution to this(to say). If you count the "e's" in sentence contained in the box, it is $8$ . But if you count them including the "e's" in the sentence above to the box, it is $11$ .