\({V}_{{y}}=72 {km} / {hr}=20 {m} / {s}\)
by doppler's effect
\({F}^{\prime}={F}_{0}\left(\frac{{V} \pm {V}_{0}}{{V} \pm {V}_{{s}}}\right)\)
\(1320={F}_{0}\left(\frac{340+20}{340-10}\right) \Rightarrow {F}_{0}=1210 {Hz}\)
(હવામાં ધ્વનિનો વેગ $330\;m/sec$ છે)