Answer:
Step-by-step explanation:
#19.
(7x - 2)° + (10 - 3x)° = 180°
(7x - 3x) + (10 - 2) = 180
4x = 172
x = 43
#21.
(6x - 144)° = (2x)°
4x - 2x = 144
2x = 144
x = 72
