The cost function is exponential, in that the variable "x" is an exponent.
This means that the value does not decrease by the same amount each year.
The 0.95 = 95% which is 100%-5% .
This means that the Cost is actually decreasing by 5% each year.
So as the Cost decreases each year, the amount it decreased by also goes down each year.
5% of 800 = 40 (800-40 = 760)
5% of 760 = 38 (760 - 38 = 722)
5% of 722 = 36.1
.... and so on