
Cecilia M. answered 10/27/20
Experienced Teacher Specializing in Mathematics for ages 3 - 50+
m∠BCD = 162°
Assume ∠BCE and ∠ECD are adjacent angles and share the line segment EC
where C is the vertex in all three angles
(Angle Additive Postulate)
m∠ECD = 5(m∠BCE) - 6
m∠ECD + m∠BCE = 162°
substitute 5(m∠BCE) - 6 for m∠ECD
5(m∠BCE) - 6 + m∠BCE = 162°
combine like terms
6(m∠BCE) - 6 = 162
get 6(m∠BCE) by itself on one side of equal sign
6(m∠BCE) - 6 + 6 = 162 + 6
6(m∠BCE) = 162 + 6
6(m∠BCE) = 168
Get unknown alone on one side of the equal sign
6(m∠BCE) / 6 = 168 / 6
m∠BCE = 28°
Plug in this measurement for m∠BCE to solve for m∠ECD
m∠ECD = 5(m∠BCE) - 6
m∠ECD = 5(28) - 6
m∠ECD = 140 - 6
m∠ECD = 134
Now check
m∠ECD + m∠BCE = m∠BCD
we know
m∠BCD = 162
m∠ECD + m∠BCE = 162°
substitute in the measurements for each angle
m∠ECD = 134°
m∠BCE = 28°
134° + 28° = 162°