https://brainly.com/question/68367When two lines intersect at a point, angles are formed. Some of these angles formed are vertically opposite and thus are equal.
Therefore, the required proof and answer to the question are stated below:
a) m< TRV = 60° (given)
  m<TRS = 4x° (given)
Thus, it can be concluded from the diagram that:
<TRV ≅ m<BRW  (vertically opposite angle property)
Also,
m<TRS ≅ m<VRW (vertically opposite angle property)
But,
m<VRW = m<VRZ + m<ZRW
Thus,
m<TRV ≅ m<BRW = 60°
m<TRV + m<BRW + m<TRS + m<VRW = [tex]360^{o}[/tex]
60° + 60° + m<TRS + m<VRW = [tex]360^{o}[/tex]
m<TRS + m<VRW = Â [tex]360^{o}[/tex] - [tex]120^{o}[/tex]
               = [tex]240^{o}[/tex]
2m<TRS = [tex]240^{o}[/tex] (since m<TRB = m<VRW )
m<TRS = 120
4x = 120
x = [tex]\frac{120}{4}[/tex]
 = [tex]30^{o}[/tex]
Thus, x = [tex]30^{o}[/tex]
b) The missing reason in step 3 is the angle addition postulate.
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