The answer is the third graph.
What ever number is for X you have to turn it into a positive. So lets say the value of X is -2, you turn it into a positive 2. Then multiply 2 by 2 to get four. So f(x) would equal positive 4.
F(x) is another way of saying Y.
Even if the pattern is only shown with 10 numbers you can solve to see what the 100th term would be with algebra
=5 + 3 + 3 * 15
do multiplication first
=5 + 3 + 45
=8 + 45
=53
ANSWER: 53
Hope this helps! :)