We need new air filters

I have to say that my wife does way more around the house than I do. Of course, I do loads of housework, laundry and cleaning. But my wife, Jill, does all of the home improvements and all of the repairs around here. I know that it might seem a little backwards, but these are our strengths. For instance, last week our air conditioning stopped working for some reason. There was just warm air coming out of all the air conditioning vents and the house just wasn’t cooling down. We had the air conditioning turned all the way down on the thermostat, but nothing was working. So, Jill went down to the basement to look at the heating system to see if she could figure out what the problem was with the HVAC system was.. I heard her messing around with the central air conditioning in the basement, but there still wasn’t any cold air coming out of the vents. Jill called up the stairs to get me to come down from the bedroom. I went downstairs to the basement and Jill was holding up a disgusting looking air filter. It was gray with dust and debris and it looked like it was completely clogged up. Jill said that it was no wonder that there was no cold air going on with our air conditioning system. She wanted to work on cleaning out and blowing all the dust and dirt out of the HVAC system and so she wanted me to go to the hardware store to pick up a new air filter for the air conditioner. I left to go to the hardware store, but when I got to the heating and air conditioning aisle, I saw that there were dozens of filters that would fit our air conditioning system. I had no idea which air filter to get, I was helpless!