Both angles are supplementary, which means that they both add up to 180°. To find the value of x, simply put the two equations together like this:
A.)

The -7 and +7 cancel each other out, which leaves us with

-->

180 is 36 times bigger than x, so divide both sides by 36:

x = 5
Now plug in the value of x:
B.)
123°
C.)
57°
To check your work, add them both up.

I hope you found this helpful. : )