SV is an angle bisector of ∠RST. If m∠RSV = (3x + 7)° and m∠RST = (8x − 12)°, find x.
 Select each definition, postulate, or theorem you will use.
 A Angle Addition Postulate
 B Linear Pair Theorem
 C definition of midpoint
 D definition of angle bisector
 The solution is x = .