Answer:
Im going to guess k is the unknown
Step-by-step explanation:
7k-14=42
42+14=7k
56=7k
56/7=k
k=8
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 />
This is really obvious but the answer is 4 feet.