Questions

Given 

1 = 1 => 1 x 11 = 11

2 = 22 => 2 x 11 = 22

3 = 33 => 3 x 11 = 33

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Similarly,

11 => 11 x 11 = 121.

Envelope is a letter holder for one letter and in the question it mean that it holds one letter. Eye is also a word which starts and end with E but has one letter in the middle.

From the assumption and trial and error method,

last three digits sum must leave the same digit as the answer. It is possible only if the answer must be units digit number leaving tens digit as carry.

And the possible 3rd digit is 5. Since 5 + 5 + 5 = 15 

Now, 2nd step is  1 + x + x + x = 5

=> 3x = 4

It is possible with x = 8. 8 + 8 + 8 + 1 = 25 leaving 2 as carry. 

Now, 3rd step is 2 + x + x + x = 5 => x = 1

Hence, the three dgits are 1, 8, 5.

185 + 185 + 185 = 555. 

The main component of bones and teeth is Calcium Phosphate.

The playground of baseball is known as Baseball Diamond or the ball field.