すみません。問題を再度整理します。
次のファイルは、re5538.texを若干修正したものです。
この結果、【解答】の行と\tyuukai環境の行の間の行間が開きすぎるので、
狭くする方法はないのだろうかという趣旨です。
また、このファイルの\usepackagae{emathBk}の部分を
\usepackage{emathAt}とすると、開きすぎずにちょうどよいのですが。


% --- re5539-Bk.tex -----------------------------------------------
\documentclass[a4j,fleqn]{jarticle}
\usepackage[notMy]{emathPh}
\usepackage{emathMw}
\usepackage{emathPb}
\usepackage{emathEy}
\usepackage{emathBk}
\usepackage{emathR}
\usepackage{showexample}
\listfiles
\begin{document}
\begin{itembox}{問題}
問題部分および地の文は，通常の\verb+\textwidth+で組まれます。
問題問題問題問題問題問題問題問題問題問題問題問題問題問題問題
問題問題問題問題問題問題問題問題問題問題問題問題問題問題問題
\end{itembox}
【解答】
\begin{tyuukai}
解答部分は\verb+tyuukai+環境内に記述します。
そこでは，右側一部が注釈のための領域となります。
これは，\verb+jquotation+環境によって実現されています。

\tyuu{注釈領域です。
注釈を付けるには，\cmd{tyuu}コマンドを用います。}
ここで注釈をつけてみます。
解答解答解答解答解答解答解答解答解答解答解答解答解答
解答解答解答解答解答解答解答解答解答解答解答解答解答
\end{tyuukai}

\verb+tyuukai+環境が終ったあとは，通常の\verb+\textwidth+幅にもどります。
地の文地の文地の文地の文地の文地の文地の文地の文地の文地の文地の文地の文
地の文地の文地の文地の文地の文地の文地の文地の文地の文地の文地の文地の文
\end{document}
----------------------------------------------------------------------------
この場合のlogファイル

------------------ re5539-Bk.log -----------------------------------------------

This is pTeXk, Version 3.141592-p3.1.10 (sjis) (Web2C 7.5.6) (format=platex 2006.12.31)  18 JAN 2007 14:07
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| | | [] 
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[1

] (./re5539-Bk.aux)

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Output written on re5539-Bk.dvi (1 page, 2792 bytes).

▼関連発言
│
└◆5538:tyuukai環境とemathAt emathBk [takao] 01/16 22:57
　├◆5539:Re:tyuukai環境とemathAt emathBk [tDB] 01/17 11:48
　│├◆5544:Re[2]:tyuukai環境とemathAt emathBk [takao] 01/17 15:21
　││└◆5545:--- [---] 01/17 15:54
　│├◆5553:Re[2]:tyuukai環境とemathAt emathBk [takao] 01/18 14:15
　│├◆5577:--- [---] 01/23 10:22
　│└◆5578:re5538.log [takao] 01/23 10:25<-last
　└◆5555:--- [---] 01/19 17:09