College Algebra
posted by Phoebe .
20. Growth of an Account If Russ (see Exercise 19) chooses the plan with continuous compounding, how long will it take for his $60,000 to grow to $80,000?
3. (1/8) to the 2x3= 16 to the x +1
13. e to the 4x= 4 to the x2
15. ln (x4) ln 3= ln(1/5) to the x power
20. Tripling Time For any amount of money invested at 6.8% annual interest compounded continuously, how long will it take to triple?
Please someone help ASAP!!!!!!!!! I don't understand any of these college algebra problems.

19
you want to solve for t
60000 e^.0675t = 80000
e^.0675t = 1.333...
ln both sides and use rules of logs
.0675t lne = ln 1.3333... ( but lne = 1)
t = ln 1.3333../.0675 = 4.26 years, appr 4 years and 3 months
3.
(1/8)^(2x3) = 16^(x+1)
(2^3)^(2x3) = (2^4)^(x+1)
2^(6x + 9 = 2^(4x + 4)
6x + 9 = 4x + 4
10x = 5
x = 1/2
13.
e^(4x) = 4^(x2)
ln both sides
4x lne = (x2)ln4
4x = ln4 x  2ln4
4x  ln4 x = 2ln4
x(4  ln4) = 2ln4
x = 2ln4/(4ln4)
= appr 1.0608
15. ln(x4) ln3 = ln(1/5)^x
no simple algebraic way to solve this, unless I misread the question. I took it the way you typed it
ran it through Wolfram and Wolfram ran out of time trying to solve it
http://www.wolframalpha.com/input/?i=solve++ln%28x4%29*ln3+%3D+ln%281%2F5%29%5Ex
20. solve
1 e^.068t = 3
now do it the same way as #19