Hall and Jorgenson uses the integral to find the present value...

z = [integral from 0 to infinite] exp(-r s) D(s) ds

Find z, so it's a function of t, when...

D(s) = 2(t - s) / t^2 for 0 <= s <= t, D(s) for s > t. (Linear decrease)

It would be appreciated a whole lot, if anyone could take a look at the above...

Good evening,

Simon DK