Answer:
B. 40
Explanation:
This is a straight angle; this means that 20 and 4x are supplementary angles.
SUPPLEMENTARY ANGLES: TWO ANGLES WITH A SUM OF 180°.

First, subtract 20 from 180 and from 20.
(cancels itself out).

Now we are left with 4x = 160.
Lastly, divide 160 from 4.

Therefore, the value of x is 40.
Here's an attachment to make this process easier to understand.