Logarithmic Function Help Please?

Question

Hello I need help with this question. Please no *do your own homework* Like I said...the book doesn't ellaborate. Thanks So Much!

The number of computers sold by BCC depends on the dollar amount, x, that they spend on advertising. How many computers will they sell by spending $40,000 on advertising? Do not include units in your answer.
N(x) = 100 + 20*ln(0.25x)

ooo sorry...wrong question. That is the answer I got for the other one though thanks. But here's the actual one...

The number of computers sold by BCC depends on the dollar amount, x, that they spend on advertising. How much must they spend to sell 300 computers? Round to the nearest dollar; do not include units in your answer.

N(x) = 100 + 20*ln(0.25x)

Answer 1

ln(0.25*40000)=9.21
N(x) = 100 + 20*9.21 = 284.2

Answer 2

As far as I can tell, this is a simple "plug and chug" problem. All you need a calculator with a "ln" key. Use 40,000 as the value of x.

Note: since there is no such thing as 0.56, or 0.033 of a computer, round your answer to the nearest whole number.

~Donkey Hotei

Additional:
Scratch all that.......

first thing you want to do, is move all the stuff outside the natural log to the left:
N(x) / 20 - 5 = ln( x / 4)

to eliminate the ln(), you need to use the fact that e^x, and ln(x) are "inverse operations," or in other words, they cancel each other; e^ln(x) = x, so taking e to the power of both sides, we get:
e^{ N(x) / 20 - 5 } = e^ln(x / 4) = x / 4

so finally,
x = 4 * e^{ N(x) / 20 - 5 }

now you can just plug and chug using 300 as the value of N(x)

Hope that makes sense......

Answer 3

88,106.