How to Number Equations in Latex with Letters?

[Madara]

Hi,
I was wondering how to number a set of equations (in Latex) under the same number but differentiate with a letter appeneded at the end!
i.e,
aX + bY = k -------(1.1a)
cX + dY = l -------(1.1b)
rX + sY = m -------(1.1c)
like wise.
I can get them numbered as (1.1),(1.2),(1.3) etc. But don't know how to get the above format.

Thanks,
Madara

 

[cristo]

Use the "subequations" environment.