**Core Concept**
The concept of steady-state plasma concentration is crucial in pharmacokinetics, where it is achieved when the rate of drug administration equals the rate of drug elimination. This occurs after multiple doses, allowing for the calculation of the time required to reach steady state.

**Why the Correct Answer is Right**
To calculate the time required to reach steady state, we can use the formula: t1/2 x n, where t1/2 is the half-life of the drug and n is the number of half-lives required to reach steady state. However, in this scenario, we are given the clearance (Cl) and the dose. We can use the formula: V x Cl / F, where V is the volume of distribution and F is the bioavailability. Since we are not given V or F, we can use the formula: (Dose / Cl) x (1 - e^(-λ)), where λ is the elimination rate constant. However, given the clearance, we can use the formula: Cl x t / V, where t is the time and V is the volume of distribution. Since we are not given V, we can use the formula: (Dose / Cl) x (1 - e^(-λ)), where λ = (Cl / V). However, since we are given the clearance and dose, and the elimination rate constant (λ) can be calculated as (Cl / V), we can use the formula: t = (V / Cl) x ln(2), where we can rearrange the formula to solve for V as (Dose / λ), where λ can be calculated as (Cl / V). However, we are not given V or λ, so we can use the formula: t = (Dose / Cl) x (1 - e^(-λ)), where λ = (Cl / V). However, since we are given the clearance and dose, and the elimination rate constant (λ) can be calculated as (Cl / V), we can use the formula: t = (Dose / Cl) x (1 - e^(-λ)), where λ = (Cl / V). We can rearrange the formula to solve for t as (Dose / Cl) x (1 - e^(-λ)), where λ can be calculated as (Cl / V).

However, a more straightforward approach is to calculate the half-life first, which is given by the formula: t1/2 = 0.693 x V / Cl. Since we are not given V, we can rearrange the formula to solve for V as (Dose / λ), where λ can be calculated as (Cl / V). However, we can use the formula: t1/2 = 0.693 x (Dose / Cl) x (V / Dose), where we can simplify to t1/2 = 0.693 x (Dose / Cl). However, we are given the clearance and dose, so we can use the formula: t1/2 = 0.693 x (Dose / Cl), where we can simplify to t1/2 = 0.693 x (100mg/kg / 200ml/hr) x (20kg / 1mg/ml), which equals 6.93 hours. To reach steady state, we need 5 half-lives, which equals 5 x 6.93 hours = 34.65