A 5-m rod has a linear density p(x) = 40e^(-x/8) kg/m, where x is the distance from one end of the rod. Which of the following definite integrals represent the total mass of the rod?
1) ∫[0,5] 40e^(-x/8) dx
2) ∫[0,5] 40e^(-x/8) dx + ∫[0,5] 40e^(-x/8) dx
3) ∫[0,5] 40e^(-x/8) dx + ∫[0,5] 40e^(-x/8) dx + ∫[0,5] 40e^(-x/8) dx
4) ∫[0,5] 40e^(-x/8) dx + ∫[0,5] 40e^(-x/8) dx + ∫[0,5] 40e^(-x/8) dx + ∫[0,5] 40e^(-x/8) dx