Question 1125095
N = 8(1+.15)^d  d is the number of days, and N is the height after d days.<P>

b.  25 = 8(1.15)^d

log25 = log(1.15)^d = dlog(1.15)


log25/log1.15 = d = 23.03 days = around 23 days.<P>

c.  Likewise for 138 inches it's log138/log1.15 = about 35 days