students in Japan go to school an average of 232+3x days, while students in the
U.S. go to school an average of 184+4x days. How many more days, on average
does a japanese student attend school each year?

First think how you would do if it had read numbers instead of algebraic
expressions.

Suppose first that it had read this way, as in the second or third grade:

Students in Japan go to school an average of 250 days, while students in the
U.S. go to school an average of 150 days. How many more days, on average does a
japanese student attend school each year?

In the 2nd grade you would go:

250 - 150 

and get 100 days.

So in algebra you go: 

(232+3x) - (184+4x) and get 100 days.

Now you remove the parentheses by sticking a factor 1 just before them:

1(232+3x) - 1(184+4x)

Then we remove the parentheses by the distributive principle:

232 + 3x - 184 - 4x

Then combine like terms

   48 - x 

Edwin