A 20 amp 240 volt circuit can provide 4800 watts.
4800 watts / 6 watt per foot = 800 feet.
about 1 foot
0.0988 per foot
12" or the length of your ruler.
The easiest way to find this out is with a tape measure: 183.5cm.
A foot is a foot, whether on a ruler or a tape measure, an odometer or laser range-finder or any other modern measuring instrument.
No, walgreens does not carry heat tape. You should be able to find some at a hardware store such as Ace Hardware or Lowes. Pricing can vary but you should be able to get some for less than $10.
With heat wrap/ heat tape, there are a few models that have a thermostat built onto the cord that keep the temp above freezing. Then you should wrap an insulation tape around the heat tape.
Heat tape is just for keeping the pipes from freezing, it does not heat the water. That's what the hot water heater is for.
It does not appear that there is any special clothing you need to buy to use heat tape. There are accessories for using heat tape, but they are not clothing related. To find out more check out Heat Tape & Accessories - Winter Weather - Ace Hardware www.acehardware.com
The purpose of heat tape is to maintain and control pipes and vessels. This also keeps the heat that is being radiated from the pipes and vessels inside.
IF she just bought 50 feet then this would be too short for even one of her 56 foot requirements.
You can find heat tape in many places. I would check www.ebay and www.amazon.com first to see if you can find some heat tape for a good price. You may also try Menard's or Lowe's.