Express the present value sums $c_{t_1}, c_{t_2},..., c_{t_n}$ due at times $t_{1}, t_{2},..., t_{n}$ in terms of the force of interest at time $t$, denoted by $\delta (t)$.
$$c_{t_1}v(t_1)+ c_{t_2}v(t_2)+\dots+ c_{t_n}v(t_n)= \sum_{j=1}^n c_{t_j}v(t_j)$$ where $v=1/(1+i)$ where $i$ is the interest.
I know that $\delta=\ln (1+i)$ and then you can sub in $v$ but it doesn't get me anywhere...