Respuesta :

Answer:

21

Step-by-step explanation:

straight line = 180 degrees ( H,D,R)

180 = 7x - 3 + 2x  - 6    

180 = 7x + 2x - 3 - 6     (group the same type number together)

180 = 9x -9           (simplify the numbers)

189 = 9x    (+9)

21 = x    (divide by 9)