Is it possible to express in a calc block some basic operations with 
variables and non-predefined units?


For example, if you wanted to build a code block that calculates how 
much money costs:

a land with an Area of 300x300 m^2 at a price of 1 $/m^2.


Would it be something like this?

#+begin_src calc
   a = 300 m
   b = 300 m
   Area = a*b
   cost = 1 ($/m^2)
   A*c

#+end_src


Is it possible to work with the "$" unit?

Why A*c won't show an arithmetic result, but ~: A c ~?

Wanted result is:


#+RESULTS:
: 90 000 $


Best regards