A hawk flying at $26$ m$/$s emits a cry whose frequency is $410$ Hz$.$ A wren is moving in the same direction as the hawk at $11$ m$/$s$.($Assume the speed of sound is $343$ m$/$s$.)$

$($a$)$

What frequency does the wren hear $($in Hz$)$ as the hawk approaches the wren?

Hz

$($b$)$

What frequency does the wren hear $($in Hz$)$ after the hawk passes the wren?

Hz