Installing Washer Dryer Hook-ups

Hello,

We’d like to install washer/dryer hook-ups for us and our two tenants. I want to know what all is involved. We have 100 amp service for each floor, so we probably have enough electricity, but do we need to upgrade the electrical recepticals in which they will be plugged? If we get gas washer/dryers do they both run on gas or partially run on gas and partially on electricity? What modifications will I need to make to the gas lines? The tenants already pay for their cooking gas – will they also also be paying for the gas used to run the washer/dryers? How much will this work cost? Has anyone else installed washer/dryers and if so, was it worth it?