\(C =\) speed of sound
\(V_{S}=\) speed of source
\(f_{2}=50=f_{0}\left(\frac{C}{C+V_{5}}\right)\)
\(\frac{f_{1}}{f_{2}}=2=\frac{C+V_{5}}{C-V_{5}}\)
\(2 C -2 V _{ s }= C + V _{ s }\)
\(3 V _{ s }= C\)
\(V _{ S }=\frac{ C }{3}\)
\(100= f _{0} \frac{ C }{\frac{2 C }{3}}=\frac{3}{2} f _{0}\)
\(f _{0}=\frac{200}{3}\)