The concepts covered in section13.6.3 for higher order differential equations can also be employed to solve system of related equations.   Consider the predator-prey models developed early part of the 20^th century in which the number of predators and preys may be predicted using the pair of ODEs

                    dn_prey/dt = an_prey - bn_preyn_predator  

                    dn_predator/dt = -cn_predator + dn_preyn_predator

where n stands for number, a is the prey growth rate, c is the predator death rate, and b and d are coefficients representing the effects of prey-predator interactions. Given a = 1.2, b = 0.6, c = 0.8, and d = 0.3, create a function similar to "twofuns" on page 526. Then use ODE45 to solve for time span of 0 to 30 given the initial number of prey is 2 and the initial number of predators is 1. You should produce a plot showing the number of prey and predators as a function of time.