Respuesta :

fieryanswererft

Answer:

x = 3

Step-by-step explanation:

The sum of interior angles in a triangle measure to 180°.

So the sum of angles = 180°

(21x - 3) + (17x + 9) + (15x + 15) = 180

21x - 3 + 17x + 9 + 15x + 15= 180

21x + 17x + 15x -3 + 9 + 15 = 180

53x + 21 = 180

53x = 180 - 21

53x = 159

x = 159/53 = 3