What is the Surname of Barbie Doll?

Two prisoners Jack and Jill are locked in a cell.
There is open window approx 40 feet above the ground of the cell.
They are never able to reach there.

Then they plan to escape by a tunnel and they start digging out.
After digging for more than 20 days, Jill comes with the different plan and they escaped.

what was the plan ?

Count the number of times the letter "F" appears in the following paragraph:

FAY FRIED FIFTY POUNDS OF
SALTED FISH AND THREE POUNDS
OF DRY FENNEL FOR DINNER FOR
FORTY MEMBERS OF HER FATHER'S FAMILY.

Replace the question mark with the correct number in below Picture:

What has six faces, but does not wear makeup, has twenty-one eyes, but cannot see? What is it?

Christina, Allison and Lena are 3 daughters of John a well-known Mathematician, When I asked John the age of their daughters. He replied "The current age of her daughters is prime. Also, the difference between their ages is also prime."

How old are the daughters?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

By removing one matchstick and adding one matchstick, can you convert the word "ZOO" to an animal name?

I am under you when I am whole.
I shift above you if you remove the first letter.
I come all around you if you remove the second as well.

Can you tell me who I am?

How many minutes are there in Feb 2017?

Note: The shortest answer is the correct answer.