We can write as,

x + (y - z) = 180

or 100 + 120 - z = 180

or z = 40
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The post above states that the answer is C, yet this states that the answer is B (40). Which is correct? Also, why did you go about solving it this way (subtracting z)? Thank you very much in advance for explaining the reasoning behind this for me

First you calculate the angle marked in red which is \(y-z\)

And the you calculate the angle marked in violet \(x+y-z\). Since the angle in violet is a straight line you can write:

\(x+y-z=180\)

Substituting the values of x and y we can obtain the value of \(z=40.\)

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Another approach is to consider the entire full rotation angle which is 360°

Now of this 360 x is 100 so z = 260 and y is 120 so z = 40°.

Z must be 40°.

Hope this helps

Regards
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