Hello there! The answer is 12.
It looks like the values on the yellow shape are 3 times greater than the values on the red shape. If the value is 4 on the red shape, the corresponding value of x will be 12 (since the angle x is in the same place in the yellow shape as the 4 is in the red shape, and 4 x 3 is equal to 12.)
I hope this helps and have a great day!
