Apparent frequency of sound heard by the observer from source is
$n_1=\left(\frac{v-v_0}{v-v_s}\right) n$
$=\left(\frac{v-u}{v+v_s}\right) n$
Apparent frequent of sound heard by the observe from source
$n _2=\left(\frac{ v + v _0}{ v - v _0}\right) n$
$=\left(\frac{ v + u }{ v - v _{ s }}\right) n$
$\text { No. of beats }=8$
$n _2- n _{ l }=8$
$\left(\frac{ v + u }{ v - v _{ s }}\right) n -\left(\frac{ v - u }{ v + v _{ s }}\right) n =8 \quad v =300, v _{ s }=0, n =660$
$\Rightarrow\left(\frac{330+ u }{300-0}\right)(600)-\left(\frac{300- u }{330+0}\right) 660=8$
$\therefore \frac{2 \times 6604}{330}=8$
$4 u =8$
$u =2 .$
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