Driving down a mountain, Tom finds that he has descended 1800 ft

in elevation by the time he is 3.25 mi horizontally away from the top of the
mountain. Find the slope of his descent to the nearest hundredth.

Here what I have

-1800 divid it by 3.25*5280ft
-1800/17160
-0.105
have done some thing wrong it does not seem to look right

Checking in my head (appx)
about a third mile down per three miles horizontal

1/3*3 appx 1/9 or .11 apx. Looks right to me. Of course it is negative, as you did.