Seconds in this case are not "time seconds", they are divisions of a degree: One degree = 60 minutes of arc, one minute = 60 seconds of arc. So 15 seconds is 15/60 of a minute or 1/4 of a minute or .25 of a minute.
N 40 39.465 is 40 degrees, 39.465 minutes. You need to add .25 minutes.
So, N 40 39.465 + .25 = N 40 39.715.
For the longitude:
W 089 34.253 = 89 degrees, 34.253 minutes, add .25 minutes to get, W 089 34.503.
Hope this helps!
Edit: Have to learn to type quicker than Stunod!