PLEASE HELP!!!!
The photic zone describes the region in which microscopic plant life receive enough light to survive. The photic zone goes to a depth where about 1% of the surface light still remains. Find the depth of the photic zone if the intensity of light (L) at a depth (d) in meters is given by L=L0e^(-0.028d), where L0 is the intensity of surface light. You may use the graphing part of your calculator for this question.
Possible answers are:
a. 124 m
b. 134 m
c. 144 m
d. 154 m
e. 164 m

Question

anonymous · Answer

I know you can use your calculator to find it but I have no idea how!!!

anonymous · Answer

L=100 per cent
LO=1 per cent

anonymous · Answer

Ok, so how can I use that to solve? :( do I plug 0.01e^(-0.028x) into my calculator???

anonymous · Answer

You have an equation, the given, as they say. It has three unknowns -- not good. We have found two of the unknowns -- better. So now with one unknown you can solve for d.$$100percent=1percente ^{-0.028d}$$

anonymous · Answer

That makes much more sense, thank you. However im not so great at solving with exponents. How do I solve? This is how I would do it but I have noooo idea.

100                                10,000
---- = -0.028d ===>   -------  = d ===> d= -357142.86
0.01                               -0.028

I know its wrong but idk why :(

anonymous · Answer

You lost your e. You can't just arbitrarily take away your e. The plants would die from lack of sunlight.

anonymous · Answer

100
----  = -0.028d    should it start like that?
0.01e

anonymous · Answer

$$100=e ^{-0.028d}$$You have to use logarithms. Who knew marine biology was so much work.$$\ln 100=\ln e ^{-0.028d}$$

anonymous · Answer

So we just forget about the 0.01?

does it turn into 
100
------  = d?  that gives me d=-3571.43
-0.028

anonymous · Answer

There is no 0.01. The percentage signs cancel leaves 100 over one which is 100

anonymous · Answer

Ok, but I still solved and got -3571.43, which is not one of my answers. I dont understand!

anonymous · Answer

May be you did something wrong$$\ln 100=- 0.028d \ln e $$

anonymous · Answer

which gives me ln (100/-0.028)???? Im sorry I  dont understand how to do these at all and I need to solve this problem

anonymous · Answer

You have the ability to find ln 100 and ln e on your calculator

anonymous · Answer

lne = 1 and ln100 =4.6, correct???

anonymous · Answer

yes

anonymous · Answer

so then I take 4.6/-0.028= -164.28, correct?

anonymous · Answer

Yes but depth is always positive, so absolute value (erase negative sign)

anonymous · Answer

So the answer is E, 164 m? Thanks

anonymous · Answer

You're pretty good.