Answer:
86.4 hours
Explanation:
Find the number of half lives to get to 10 % ( or .10) remaining
.10 = (1/2)^n log both sides to get ( n = number of half lives)
log (.1) / log (1/2) = n to find n = 3.321 half lives
3.321 half lives * 26 hr / half life = 86.4 hours
