The equation for an exponential deprecation model like this is , where a is the starting value, x is the number of years passed, and r is the amount the value deprecates each year.
We know what a and r are: a = 1600, as that is the original cost of the computer, and r = .18, as that's how much it decreases by. Substitute these two into the equation.
We get . Now, subtract 1 - .18 to get our final answer.