The value of the missing length is 20
Let the missing length be x
From Parallel lines and transversal theorem, we have that
If three or more parallel lines intersect two transversals, then they cut off the transversals proportionally.
Then, we can write that

∴ 
x = 20
Hence, the value of the missing length is 20
Learn more here: brainly.com/question/24258397
Answer:
-12
Step-by-step explanation: