lequel,à + lequel,de + lequel

• Lequel, which usually means which
• Lequel has four basic forms, because it has to agree in gender and number with the noun it replaces.
• lequel has several contracted forms - like the definite articles le and les, lequel contracts with the prepositions à and de

• C'est un film à la fin duquel tout le monde pleure.It's a film at the end where everyone is crying.

• Leur maison ,près de laquelle coule la Marne, est un peu humide.Their house, near which flows the Marne, is a little wet

• La cheminée, au-dessus de laquelle est posée la statuette, est très ancienne.The fireplace, above which is placed the statue is very old.

http://french.about.com/od/grammar/a/lequel.htm
http://www.tolearnfrench.com/cgi2/myexam/voir2r.php?id=56380

Singular		Plural
	Masculine	Feminine	Masculine	Feminine
Forms	lequel	laquelle	lesquels	lesquelles
à + lequel	auquel	à laquelle	auxquels	auxquelles
de + lequel	duquel	de laquelle	desquels	desquelles