Answer:
x = 5
Step-by-step explanation:
a) The third interior angle of this triangle is 180 - 20 x.
The three interior angles must sum up to 180 degrees.
Therefore, 60 + 7x + 5 + 180 - 20x = 180, or
65 + 180 - 13x = 180, or
65 - 13x = 0
Finally, 13x = 65, and so x = 5
