\({\mu _1} = \tan {i_B} = \frac{4}{3}\)
From triangle \(ABC,\)
\(\tan (90 - {i_B}) = \frac{{BC}}{{AB}}\)
\(\cot {\mkern 1mu} {i_B} = \frac{{10}}{x}\)
\(\frac{3}{4} = \frac{{10}}{x}\)
\(x = \frac{{40}}{3} = 13{\mkern 1mu} \,m\)
From triangle \(AEF,\)
\(\tan (90 - {i_B}) = \frac{y}{{50 - x}}\)
\(\cot {i_B} = \frac{y}{{50 - 13}}\)
\(\frac{3}{4} = \frac{y}{{37}}\)
\(y=27\;m\)