Question 104951
The assumption is that the depreciation rate is linear. 
2 yrs after = $14,300 
4 yrs after = $10,200
Depreciation Rate = DR
DR=(Value(2)-Value(1))/(Time(2)-Time(1))
DR = ($10200-$14300)/(4-2)yr
DR = -$2050/yr. 
The negative rate means that you lose value as time goes on, that is,  depreciates. 
If you look at the DR equation, it looks like a slope calculation. 
In fact, the rate is the slope of the value function, V(t). 
Let's find the intercept. 
{{{V(t) = mt+b}}}
{{{V(t) = -2050t+b}}}
At 2 years,
{{{V(2) = -2050(2)+b = 14300}}}
{{{b=14300 + 2(2050)}}}
{{{b=18400}}}
{{{V(t)=18400-2050t}}}
At t=0 years, the car is brand new and its value was $18,400. 
When V(t)=0, what will t be?
{{{18400-2050t=0}}}
{{{-2050t=-18400}}}
t=8.97 years, almost 9 years old.