40/3=x???

Charlie got hired to help a lady rake leaves.  He was there for 3 hours.  When I went to pick him up, he proudly pulled out an envelope that contained $40 and showed it to me.  This seemed like the perfect time to do some real-life math.  (Charlie has trouble with word problems and scenario type math.) 

"So if you worked for 3 hours and earned $40, how much did you make per hour?"

He gives me a strange look.  "I don't have the calculator with me." 

"You don't NEED a calculator.  This is simple math; you can do it in your head."

He sits and thinks for a minute, and then he leans forward and starts WRITING IN THE DUST on the dashboard of the car....and still got the wrong answer.

So my question is, does this make a stronger statement about his failure to master word problems, or my failure to clean the car? 

The equation is still there, by the way.