How do you go from 98 to 720 using just one letter?

In a secret society, a buried chamber can be accessed only via a secret password. The password is seven characters long and comprises of just letters and numbers.

You find a code that can help you in cracking the password. The code says "You force heaven to be empty".

Can you deduce the password from that?

Can you count the number of seconds in a year?

Clue: You need to bother about calculation.

Rearrange the letters in "new door" to make one word.

Can you find the missing number in the third row?
35 20 14
27 12 18
5 2 ?

What is always in front of you but can’t be seen?

A man is walking down a road with a basket of eggs. As he
is walking he meets someone who buys one-half of his eggs
plus one-half of an egg.
He walks a little further and meets another person who buys
one-half of his eggs plus one-half of an egg.
After proceeding further he meets another person who buys
one-half of his eggs plus one half an egg. At this point, he
has sold all of his eggs, and he never broke an egg.
How many eggs did the man have to start with?

I have an eye but still cannot see.

Who am I?

I am a type of food that is often found in the fridge and can be white in colour. What I am?
Hint 1: I am a dairy product.
Hint 2: You can spread me on the bread.

Why is it very easy to weigh a fish?