Answer:
x = 19
Step-by-step explanation:
(5x + 4)° + (x - 2)° + (3x + 7)° = 180°
(5x + x + 3x)° + (4 - 2 + 7)° = 180°
9x° + 9° = 180° → ÷9
x + 1 = 20
x = 20 - 1
