Answer: The Answer is 7, Hope this helps! :)
Step-by-step explanation: We know that 6 and 12 are related, 6 times 2 is 12 so if you do the same for 4 and you multiply 4 by 2 you get 8 for the blank side, then subtract 1 from 8 to get 7. Same for the bigger triangle, 6 times 2 is 12 subtracted by 1 is 11.
So final answer is 7 for X!