### 5.3 Numbers as Units

For `units`, numbers are just another kind of unit. They can
appear as many times as you like and in any order in a unit expression.
For example, to find the volume of a box that is 2 ft by 3 ft by 12 ft
in steres, you could do the following:

You have: 2 ft 3 ft 12 ft
You want: stere
* 2.038813
/ 0.49048148
You have: $ 5 / yard
You want: cents / inch
* 13.888889
/ 0.072

And the second example shows how the dollar sign in the units conversion
can precede the five. Be careful: `units` will interpret
‘`$5`’ with no space as equivalent to ‘`dollar^5`’.