4. The concentration x(t) of certain chemical in human body at time t (measured in hours) after an injection satisfies the differential equation
dx (t2 + 1) dt = z2 + 1).
If the initial concentration ( at the time of injection) is given by x(0) = 4 , find the concentration after one hour. (20 points) This is the exact same differential equation with in-class problem 3 for section 1.3.