[a] How did the authors separate the expressiony t/-t'y(The text shows the result. Show or explain the algebra that was used to get there.)[b] Why does the author claim that the solution is only valid for -1< t <1?c) If x(t) is amount of salt in a tank at time t, then the general model for the rate of change of the amount of salt in the tank is dx/dt=? Use words not symobols for answer