Builder and Rollo are CORRECT
Working backwards, on the 4th day they cover 1/2 of the remainder - if the distance after the 4th day is 14 miles, they must cover 14 miles on the 4th day ( a half of what was remaining after day 3).
On the 3rd day they cover "2-fifths of the remainder", so the balance after day 3 (28 miles) must represent 3-fifths of what is remaining after day 2. So the distance travelled on day 3 is 18.667 miles, which represents 2-fifths of the distance remaining after day 2.
On the 2nd day, they covered "a 1/4 of what's left". We know that the balance after day 2 is 46.667 miles (28 + 18.667).
This must represent 3-quarters of what is left after day1, so on day 2, they cover 15.556 miles (1/3 of 46.667).
On day 1, they cover "1/5th of the total distance". We know that the balance at the end of day 1 is, as calculated, 62.223 miles and this is 4/5ths of the total distance - so they cover 15.556 miles again, being 1/5th.
So, I think that the total distance is 77.779 miles BUT that is not what is asked. The question asks "How far have they travelled?" and the facts do not state that they have travelled the complete distance- they were left with 14 miles, so, as Rollo and Builder said, they travelled 63.779 miles !!