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Answer:
D. Can't be determined
Explanation:
You know that the sum of angles in a triangle is 180°, so ...
a + x + 60 = 180
b + y + 40 = 180
Then the difference between 'a' and 'b' is ...
a - b = (120 -x) -(140 -y) = y -x -20
Since the values of x and y are unknown, the relative values of a and b cannot be determined.
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Additional comment
If you know the triangles are similar (or congruent) and that the relative angle sizes are as they appear to be, then you could say a=b. There is nothing in this problem statement to indicate that is the case.