Kiley went 5.7 km/h north and then went 5.8 km/h west. from start to finish, she went 8.1 km/h northwest.

Yes, that's a reasonable rounded value for the solution.

     (5.7)² + (5.8)²  =  (32.49) + (33.64)  =  66.13

       √66.13 = 8.132...

                   =  8.1 when rounded to the nearest tenth.

The solution ' 8.1 ' is a reasonable rounded value, but only
if the question is changed to say 'km' at every place where
it now says 'km/hr'.

If 'km/hr' is correct, then there's no way to calculate Kiley's
effective northwesterly speed, using only the given information. 

We don't know how long she traveled north at 5.7 km/hr,
and we don't know how long she traveled west at 5.8 km/hr. 
So we don't know the distance between her start and end
points, and we don't know how long she traveled altogether ...
exactly the two numbers we need in order to calculate her
average speed.  Or even, for that matter, the average direction
of her trip from start to finish.

Hahahahaha nice. my guess would be age or they moved the grocery store. ; ) and remind him next time you are late getting home that it takes a long time to go 12miles, hahahave a good one!