If it increases by 15% it becomes 115% of what it was before. To take 115% of 
something is to multiply it by 1.15.  So we want to know how many times
we must multiply $8000 by 1.15 until it just becomes $16000, or first exceeds
it.  Let that number be n.  Then to get the approximate nu,ber of years



Take the log of both sides:









Divide both sides by 





or in 4 years it would be under $16000 and in 5 years
it would be over $16000.

Edwin