I solved this one in 11 minutes when I did the test.
The code is very simple if you know some basis of this type of questions.
I explain.
Look at the numbers.
63 54 65 96
This is not a ordinary line of numbers, usally the numbers is in some kind of orders, like small number first and then large numbers, like
1 1 2 3 5 8 13
This one is simple
1+1=2
2+1=3
3+2=5
5+3=8
8+5=13
and finally 13+8=21
First of all try to find some kind of order, here is one, the last number in 63 54 65 96
is 3 4 5 6
Hmm here you have some clues, maybe..............