Suppose traffic volume on a particular road has been as shown below

Year Vehicles
1970 40,000
1980 60,000
1990 90,000
2000 135,000

a) find the discrete- dynamical system. (I got this....2Vt-1/2Vt)
b)what is the traffic volume of 1960? (Got this also.... 26,667 vehicles..rounded)
c)Find the doubling time of traffic expressed in years (NO IDEA WHAT TO DO!!!)-Please Help
Showing me by steps would be wonderful!! I really have no idea what to do for doubling time...
PLEASE HELP!!!
The answer is 17 years but i have no idea how the book got this...

First off, I don't really like your formula for part (a), but I don't know how you've been taught discrete- dynamical systems so perhaps it's ok. Anyway, it multiplies by 1.5 every 10 years.

Your answer to (b) is correct.

For (c), note the volume multiplies by 1.5 every 10 years. So you need some sort of exponential. i.e.
v = u * 1.5^(t/10)
i.e. u (or v0) is the volume at year 0
v is the volume t years later.
* = multiply

So you want to find how long it takes to double the volume, so set v = 2u:
2u = u * 1.5^(t/10)
now take logs (any base, it doesn't matter as long as you are consistent)
=> log(2u) = log(u * 1.5^(t/10))
=> log(2) + log(u) = log(u) + log(1.5^(t/10))
=> log(2) = log(1.5^(t/10))
=> log(2) = (t/10) log(1.5)
=> t/10 = log(2) / log(1.5)
=> t = 10 log(2) / log(1.5)