(a) Convert the third order equation $\frac{d^3 u}{d t^3}+3 \frac{d^2 u}{d t^2}+4 \frac{d u}{d t}+12 u=0$ into a first order system in three variables by setting $u_1=u, u_2=\dot{u}, u_3=\ddot{u}$. (b) Solve the equation directly, and then use this to write down the general solution to your first order system. (c) What is the dimension of the solution space?