Work Shown:
A = P*(1+r)^t
A = 21450*(1+(-0.08))^5
A = 21450*(1-0.08)^5
A = 21450*(0.92)^5
A = 21450*0.6590815232
A = 14137.29867264
A = 14,137.30
Notice how I used a negative r value to indicate depreciation rather than growth.
