What is common among 11, 69, and 88?

Using the clues below, what four numbers am I thinking of?

The sum of all the numbers is 31.
One number is odd.
The highest number minus the lowest number is 7.
If you subtract the middle two numbers, it equals two.
There are no duplicate numbers.

Which word does the below Plexor means ?

Find the number of squares in the below picture

An express train takes 3 seconds to enter the tunnel which is 1 km long.
If it is travelling at 120 km an hour, how long will it take to pass completely through the tunnel?

What happened when the wheel was invented?

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

I don't get anymore wetter, no matter how much rain falls on me.

Sally lives in a place where six months of the year is mild summer and the temperature drops significantly the other six months. She owns a lake where there is a small island. She wants to build a house on the island and needs to get materials there. She doesn’t have a boat, plane, or anything to transport them to the island. How does Sally solve this problem?

How many pluses should we put between the digits of 987654321 to get a total of 99, and where?