Answer:
 

Explanation:
The measure of each angle in an equilateral triangle is 60°.
 (7x -3)° = 60°
 7x = 63 . . . . . . . divide by °, add 3
 x = 9 . . . . . . . . . .divide by 7
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You can tell the triangle is equilateral because all sides are marked with the same mark. That means they are the same length.