Can you replace the question mark with the correct number?

Let's play a word game. Following are some meaningless words that can be completed by adding random letters on either side of the word.

For example, the word "rdo" can be formed into "pardon".

Using the same technique, can you complete the given words?
ecalc
airb
rinci
tibac
uidel
gorit
igna
eyho

There is one four-digit whole number n, such that the last four digits of n2 are the original number n

There are two candles. Both will only burn exactly for an hour. How will you use these two candles to measure forty-five minutes?

There is a shop where written:
Buy 1 for $1
10 for $2
100 for $3
I needed 999 and still only paid $3. How could this be financially viable for the shop-keeper?

Take one out and scratch my head, I am now black but once was red. What am I?

Without looking at a calendar, within a minute name, a boy's name using 5 consecutive 1st letters of 5 consecutive months

The day before yesterday I was 25 and the next year I will be 28. This is true only one day in a year. What day is my birthday?

If your uncle’s sister is not your aunt, what relation is she to you?

If you say my name, I will no longer exist. What am I?