Answer:
a = 21, b = 1, c = -0.12, d = 3
The value after 3 years = $14.31
Explanations:
Depreciation rate, c = -12%
c = 12/ 100 = -0.12
The initial value of the car, a = $21000
The number of years, n = 3
The value of the car after 3 years, y:
y = a ( b + c)^d
y = 21 ( 1 + (-0.12) ) ^3
a = 21, b = 1, c = -0.12, d = 3
The value after 3 years
y = 21 ( 1 - 0.12)^3
y = 21 (0.88)^3
y = $14.31