計左好耐.. 幫幫我

(a)Find the general solution of the differential equation
t dv/dt –v = t, t>0
And hence show that the solution can be written in the form v = t (ln t +c) , where c is an arbitrary constant.
(b)This differential equation is used to model the motion of a particle which has speed v ms^ -1 at time ts. When t = 2 the speed of the particle is 3 ms ^ -1. Find, to 3 significant figures, the speed of the particle when t = 4.