Answer:
Step-by-step explanation:
e^ lnx = x
e^ ln5 = 5
e^ ln 3x = 3x
I think you get the idea... e is an inverse operation to ln :o
Remember that the general decay equation is:

where

is the amount after a time


is the initial amount

is the the decay percent in decimal form
The first ting we are going to do is find

by dividing our <span>decay rate of 25% by 100%: </span>

.
We also know from our problem that

. Lets replace

and

in our formula:


We know now that our decay rate is 0.75, and since 0.75<1, we can conclude that
this situation represents exponential decay.
Now, to find the initial amount, we are going to solve our equation for

:


Notice that

will depend on the number of ours

. <span />
Let the total bill be x. We have:
<span>0.15x > 21 <-- Since 15% is 0.15 using inequality calc. x </span>>$140
Step-by-step explanation:
u know u can download math go and u just take a picture and it will give u the answer