The default print setting on the library computers is double-sided. If you want to print single-sided you will need to change the default setting. In most cases you can do this by clicking on "Properties" in the printer pop-up box and unchecking the box that says print on both sides. If that is not available, ask Library or Tech staff for help.
NOTE: Two black & white pages printed double-sided are charged as one page ($0.03).