This at 40 mph still should be the same right? 965.6064/40 = 24.14016???

Be careful with units! Your original formula was:

\(\displaystyle \frac { 600 \ miles }{40 \frac {miles}{hour} } = 15 \ hours\)

When you converted 600 miles to Km, but did not convert 40 miles per hour to kilometers per hour, what you get is this:

\(\displaystyle \frac { 965 \ Km} {40 \ miles/Hr } = 24.1 \frac {Km-Hr}{mile} \)

Don't know about you, but this is not a unit of time I'm used to! You need to convert 40 MPH to kilometers per hour, which is 64.4 KPH:

\(\displaystyle \frac {965 \ Km}{64.4 \ Km/Hr} = 15 \ Hr\)

Hope this helps.