Given that,
A population p of migrating butterflies changes over time it is represented by the equation
Where w is number of weeks.
To find,
The population after 2 weeks.
Solution,
We have,

Put w = 2 in the above equation.

So, the population after 2 weeks is 64000
.
If C = 7, You would do 7-2 = 5
Cccccctttttttt
or
cccccc
---------------
tttttttttttttt
It descended 240 feet 12*20 is 240