Amodel length of 12 cm. represents an actual length of 102 ft. what is the scale for the model.

H a tough one, but it is relatively easy.  What you need to do is create a proportion for 12 cm and 102 ft.  After that, you cross multiply and turn 
the problem into an algebraic equation of 12x = 102 (I used x for the variable)
So, you divide 102 by 12 giving you the awnser of 8.5 ft.  Here is the scale:
1 cm : 8.5 ft
I hoped this helped!