An eagle flying at $38$ m$/$s emits a cry whose frequency is $540$ Hz$.$ A blackbird is moving in the same direction as the eagle at $10$ 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?

Hz

$($b$)$

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

Hz