4. In Fig. 6.31, if PQ ST, PQR = 110° and RST = 130°, find QRS.
[Hint : Draw a line parallel to ST through point R.]
Draw a line EF parallel to the ST through R.
Since PQ || ST and ST || EF
EF || PQ
PQR = QRF = (Alternate interior angles)
QRF = QRS + SRF .............(i)
Again, RST + SRF = (Interior angles of two parallels ST and RF)
(RST = , given)
Thus, QRS =