Farmer Bill is preparing his fields for planting. As he cultivates them using his equipment, a big factor in how long it takes is how dry or wet the fields are from rain. Assuming a rain fall of 1 inch, consider the following: If it has rained in the last 24 hours, he cannot cultivate his fields properly. If it rained two days ago, it takes 10 hours to cultivate about a third of his fields. If it rained three days ago, he can cultivate about half of his fields in the same 10 hours. As each day without rain passes, he can work the ground proportionally faster. Thus, the ratio of field space prepared after 2 days compared to 3 days without rain is proportional to the ratio of field space prepared after 3 days compared to four days without rain. Express the portion of his field space that he can prepare in 10 hours if it has been 4 days since it rained.

Instruction: Write it as a simplified fraction in the box below in the format a/b (without spaces).