Answer
$f'=971$ Hz
Work Step by Step
To find the apparent frequency of the sound, use the Doppler effect equation, which is $$f'=f(\frac{v \pm v_o}{v \mp v_s})$$ Since the source is moving away, the apparent tone must be lower than the actual tone. Substituting values into the equation using $v=330m/s$ yields $$f'=(1000Hz)(\frac{330m/s}{330m/s+10m/s})=971Hz$$
