When it was bought new, the time was t = 0 years and the value was $12,000.

After t = 8 years and the value is $2000.

This amounts to finding the equation of a line that passes through the two points (0, 12,000) and (8, 2000), where x represents the time and y represents the value of the computer.

m = (y2 - y1)/(x2 - x1)

where (x1, y1) = (0,12000) and (x2,y2) = (8,2000)

m = (2000 - 12000)/(8 - 0)

m = - 1250

Now we use the point-slope formula:

y - y1 = m(x - x1)

y - 12,000 = - 1250 (x - 0)

y = 12,000 - 1250x

12,000 - 1250x >=0 since the value can not be negative

x <= 9.6

We now change y to V for value, and x to t for time

V = 12000 - 1250t where 0 <= t <= 9.6

and this is the equation that gives the value V of the computer t years after purchase.