What will be the value of settling time if the final value is supposed to be 5% of desired value?

What will be the value of settling time if the final value is supposed to be 5% of desired value?

a. 2 times of time constant
b. 3 times of time constant
c. 4 times of time constant
d. 5 times of time constant

Correct Answer : b. 3 times of time constant

Explanation :

It is the standard form of settling time estimation (either 2% or 5%) in correspondence to the time constant value, but most probably 2% is taken into consideration whose value is supposed to be 4 times of the time constant.