Answer:
[tex] r \perp s, \: t \perp s \\ \angle 3 = \angle 4 = \angle 5 = \angle 6\\ [by \:definition\: of \perp \:lines]\\ so, \: \angle 3 = \angle 6 \\ \because \:the \:two \:alternate \:angles\: are \:equal \\ \therefore r\|t [/tex]
