Answer:
C, I think.
Explanation:
If it goes down at a constant rate over 5 years and ends on $0, $420 is the amount it goes down by (divide 2,100 by 5 to check). So if 2 years pass, that 2 $420's, or $840, I think. If you take that away from 2,100, that's the amount the computer still values.