Coded Messages

(Notice the $ sign and the NO sign)

Dear Father,

$chool i$ really great. I am making lot$ of friend$ and $tudying very hard. With all my $tuff, I $imply can't think of anything I need, $o if you would like, you can ju$t $end me a card, a$ I would love to hear from you.

Love,
Your $on.

After receiving his son's letter, the father immediately replies by sending a letter back.

Dear Son,

I kNOw that astroNOmy, ecoNOmics, and oceaNOgraphy are eNOugh to keep even an hoNOr student busy. Do NOt forget that the pursuit of kNOwledge is a NOble task, and you can never study eNOugh.

Love,
Dad