Answer
$\approx73.68°$
Work Step by Step
There are $60$ seconds in $1$ minute.
Hence
$40"=\frac{40}{60}'=0.6667'$
Hence
$73°40'40"=73°(40+0.6667)'$
$=73°40.6667'$
There are $60$ minutes in $1$ degree.
Hence
$40.6667'=\frac{40.6667}{60}°=0.6778°$
Hence
$73°40'40"=(73+0.6778)°$
$\approx 73.68°$ (to two decimal places)