first day
ok so 4 inches up means 4 iches above the bottom, 10% of 4 is 0.4, and 4-0.4=3.6
second day
3.6+4=7.6, now 10% of that is 0.76, 7.6-0.76=6.84
third day
6.84+4=10.84, 10% of 10.84 is 1.084, 10.84-1.084=9.756
fourth day, at begining is at the end of third
worm is 9.756 in above the bottom of hole
20-heightup=height from top
20-9.756=10.224
answer is 10.224 inches from top