Does anyone know which one it is?
or how to do it/ walk through.

We know, the sum of all the angle in an triangle is 180, 
So, We can calculate adjacent angle of angle 1, 

Let, that adjacent angle = b
So, 34 + 103 + b = 180
b = 180 - 137
b = 43

Now, angle b forms linear pair with angle a, so their sum would be 180
a + b = 180
a + 43 = 180
a = 180 - 43
a = 137

In short, Your Answer would be Option C

Hope this helps!