All you have to do is turn one of the numbers from yards to feet or feet to yards, so you can accurately add it. Considering it would be easier to turn the yards to feet, you use the fact that, 1yard = 3feet. So the 6 7/12 as feet is 19.75 feet. So now you multiply them and 3 1/6 times 19.75 is 62.5416666535, and you can round this to just 63.