Question

The force of interest measured in years is given by: 𝛿(𝑡) = { 0.04 0 < 𝑡 ≤ 5 0.008𝑡 5 < 𝑡 ≤ 10 0.005𝑡 + 0.0003𝑡 2 10 < 𝑡 (i) Calculate the present value of a unit sum of money due at time t = 12.