Can you replace the question mark with the correct letter?

6 + 6 + 6 = N
7 + 7 + 7 = E
8 + 8 + 8 = R
0 + 0 + 0 = ?

A swan sits at the center of a perfectly circular lake. At an edge of the lake stands a ravenous monster waiting to devour the swan. The monster can not enter the water, but it will run around the circumference of the lake to try to catch the swan as soon as it reaches the shore. The monster moves at 4 times the speed of the swan, and it will always move in the direction along the shore that brings it closer to the swan the quickest. Both the swan and the the monster can change directions in an instant.
The swan knows that if it can reach the lake's shore without the monster right on top of it, it can instantly escape into the surrounding forest.

How can the swan successfully escape?

Count the number of squares in the picture below.

Can you solve this picture maths equation?

When 99 is considered higher than 100?

Can you solve this amazing hard number series problem?
7, 8, 10, 12, 16, 18 ?

What is the largest amount of money that you can possess in change and still if someone asks you for a dollar, you won't be able to give?

I live in a bowl. I can swim. I have a tail. I also have fins and big eyes. What am I?

Why is a river so rich ?

The centre of the third figure is empty. What digit should fit inside?