The block diagram of a system with a proportional controller is shown below

A unit step is introduced in the set point. The value of K${_c}$ to provide a critically damped response for U = 0, $\tau{_p}$ = 8 and $\tau{_m}$ = 1 is

1. 3.34
2. 2.58
3. 1.53
4. 1.12