2. a. Find the closed-loop/system transfer function of the block diagram in Figure 1. Show your calculation. X(s)- 1 1 Y(s) K s3+25s +15s+20 1 Figure 1 b. Write down the characteristics equation of the feedback control system in Figure 1. (5 points) c. Use the Routh-Hurwitz criterion to determine the range of K so that the system is asymptotically stable.