The fifteenth video, knock knock

this one is simple, and you can screw up
it's a knock knock joke
and what you see is a tank
knock knock, thank who?
no punctuation in the answer
the answer is www.thisisnottom.com/yourewelcome (highlight to expose)

read the source code
there's a link
gray.css
i got this one by luck
i typed in the first thing that i saw
which is the background code
add gray.css to the end of the url
the code/answer is "#c2c0c0"

looking at the freecell page on wikipedia will help you
look at the url it's x/times
this is a math puzzle
all of the 3 pages make up ' x time y plus z'
you got find what the numbers are
add the answer to the end of the url
the answer is -23647 (highlight to expose)

P.S. As you may already know, ThisIsNotTom was created by John Green back in 2009. He's now a best selling author. The movie The Fault In Our Stars was based on a book by him. If you liked TINT and also The Fault in Our Stars, you should check out the book that made me cry when I was supposed to be a super macho teenage boy, Looking for Alaska. You can get it here.