Line up the decimal points: 

   45.6
   -8.75

Stick on a 0 at the end of the top number so it will
stick as far to the right as the bottom number:

   45.60
   -8.75
   38.85

I didn't go into the details of how to borrow from the 6
making the 0 into a 10, etc.  If we need to do that, post 
again asking how.

Edwin