Question 55055
The problem asks you to find a linear funtion: let's call it {{{f(t)}}}.
We know its a line, so it can be of the form {{{f(t)=mt+b}}} (That's slope-intercept form there). 

What do we know? 
We're calling {{{t}}} the age of the computer. In '99, we're at {{{t=0}}} and the computer is worth $3000; in '01 {{{t=2}}}, the computer is worth $500.

Ok, so we have these two points:
(0,3000)
(2,500)

Let's plug the first point into that slope-intercept form of our line:
{{{3000=m(0)+b}}}
The m term drops away and we're simply left with 
{{{3000 = b}}}

Great. Now lets plug the second point into our equation (we know b now as well)

{{{500 = m(2) + 3000}}}}
If we subtract 3000 from both sides, we get
{{{-2500 = 2m}}}
and divide by 2
{{{-1250 = m}}}

Throw it all together, we get {{{f(t) = -1250*t+3000}}}

We can eve graph it:

{{{graph(300,200, -1,4,-1000,4000, -1250*x+3000)}}}