This can be solve by using the formula
D = P( 1 – i)^n
Where d is the depreciation value after n years
P is the initial value
i is the depreciation rate
n is the years
D = 1/3 ( 1800)
D = 600
So
600 = 1800 ( 1- 0.45)^n
Solve for n
N = 1.83 years