First look at four examples using numbers.  That way we can figure
out how to do the problems, and then we'll do the same thing using
the letters that stand for numbers:

If 3 pencils cost 12 cents, then 1 pencil would cost 4 cents,
because I divided 12 by 3 and got 4, so 8 pencils cost 32 cents,
because I multiplied 4 by 8 and got 32 cents.

If 4 pencils cost 20 cents, then 1 pencil would cost 5 cents,
because I divided 20 by 4 and got 5, so 19 pencils cost 95 cents,
because I multiplied 5 by 19 and got 95 cents.

If 6 pencils cost 12 cents, then 1 pencil would cost 2 cents,
because I divided 12 by 6 and got 2, so 11 pencils cost 22 cents,
because I multiplied 2 by 11 and got 22 cents.


If 12 pencils cost 60 cents, then 1 pencil would cost 5 cents,
because I divided 60 by 12 and got 5, so 13 pencils cost 65 cents,
because I multiplied 5 by 13 and got 65 cents.

Therefore:

If  pencils cost  cents, then 1 pencil would cost  cents, 
because I divided  by  and got , so  pencils cost  cents,
because I multiplied  by  and got  cents.

Edwin