Answer
840 Hz
Work Step by Step
Speed of sound($v$) when T=$0^{\circ}$C is 331 m/s.
Speed of the observer($v_{o}$)= $60\,km/h=\frac{60\times10^{3}\,m}{3600\,s}=16.66667\,m/s$
Frequency of the source $f_{s}=800\,Hz$
For observer moving toward stationary source,
Frequency heard by the person
$f_{o}=(\frac{v+v_{o}}{v})f_{s}=(\frac{331\,m/s+16.66667\,m/s}{331\,m/s})800\,Hz=840\,Hz$
