Note, that water on the right side of the equation should not be there - it is not a product, this water just happens to sit in the same place where your product (acetylene) is.
AWK: you are right it can be done this way. In fact that's how I calculated it at first. However, kemmy was all the time cofused and asking how to find water amount, so I decided to show him (her?) how to deal with the water problem.
BTW, have you noticed how proportionalities are often unknown to the posters?