An eagle flying at $26$ m$/$s emits a cry whose frequency is $440$ Hz$.$ A blackbird is moving in the same direction as the eagle at $11$ m$/$s$.($Assume the speed of sound is $343$ m$/$s$.)$

$($a$)$

What frequency does the blackbird hear $($in Hz$)$ as the eagle approaches the blackbird?

It looks like you made a sign error. Remember the general Doppler equation is

f$\text{'}=$

f$($v $+$ vO$)$v $$ vS

$,$

and in this case the source $($the eagle$)$ is moving towards the observer $($the blackbird$),$ and the observer is moving away from the source, so what does this tell you about vO and vS$?$ Hz

$($b$)$

What frequency does the blackbird hear $($in Hz$)$ after the eagle passes the blackbird?

It looks like you made a sign error. Remember the general Doppler equation is

f$\text{'}=$

f$($v $+$ vO$)$v $$ vS

$,$

and in this case the source $($the eagle$)$ is moving away from the observer $($the blackbird$),$ and the observer is moving towards the source, so what does this tell you about vO and vS$?$ Hz