Solution (By Examveda Team)
$$\eqalign{
& {\text{sec}}\left( {4x - {{50}^ \circ }} \right) = {\text{cosec}}\left( {{{50}^ \circ } - x} \right) \cr
& {\text{sec}}\left( {4x - {{50}^ \circ }} \right) = {\text{cosec}}\left( {{{90}^ \circ } - \left( {{{40}^ \circ } + x} \right)} \right) \cr
& {\text{sec}}\left( {4x - {{50}^ \circ }} \right) = {\text{sec}}\left( {{{40}^ \circ } + x} \right) \cr
& 4x - {50^ \circ } = {40^ \circ } + x \cr
& 3x = {90^ \circ } \cr
& x = {30^ \circ } \cr} $$
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