Question 666657
<pre>
It's the 19 that you want to make less.  So to make the 19 
K less than it is, you subtract K from the 19.

So you write down 19 and then subtract K from it like this:

19-K   green cars.

That's all you can say because there may be some brown cars,
and some yellow cars among the 30 others, and you are not told
how many of those there are, if any. 

Edwin</pre>