Which number should replace the question mark?

Considering the below equation:

V + II - VI = 10
IV - X + VIII = 20
IV - VII + VI = 30

Then, I + II + III = ?

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.

Can you place six X (crosses) in below board without making three in a row in any way ?

Do you know who was buried in John's tomb?

Katniss and Peeta are liars. They both lie on some specific days.

Katniss lies on Fridays, Saturdays and Sundays. She speaks the truth on all other days.

Peeta lies on Tuesdays, Wednesdays and Thursdays. He speaks the truth on all other days.

Can you tell that one day of the week when both of them will say "Tomorrow, I will lie."?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?

What is common among 11, 69, and 88?

Find the next number in the series below

21 32 54 87 131 ?