m∠4 = 66° (option C)
Step-by-step explanation:
m∠4 = (x + 9)°
m∠2 = (2x)°
m∠4 + m∠2 = 180° (sum of angles on a line)
(x + 9)° + (2x)° = 180°
Expand the bracket:
x + 9 + 2x = 180
collect like terms and subtract 9:
x + 2x + 9-9 = 180 - 9
3x = 171
divide both sides by 3:
3x/3 = 171/3
x = 57
m∠4 = (x + 9)°
m∠4 = 57 + 9 =
m∠4 = 66° (option C)