ANSWER
1 year and 10 months or 1.8 years
Step-by-step explanation
We have that the price of the new computer is $2100 and it decreases by 50% annually.
This means it is a compound decrement.
So, we can apply the formula:

where A = price after t years
P = initial price
R = rate of decrease
t = amount of years
Therefore, we have that:
A = $600
P = $2100
R = 50%
Therefore, we need to find t:

The computer will have a value of $600 after 1 year and 10 months.