The time required for $100 \%$ completion of a zero order reaction is

What is the concentration (in $mol \ L^{-1}$) of the product $B$ after $20 \ s$ in the following reaction? Given that $A \longrightarrow 3B$,rate $= k[A]^0$. The data is provided in the table below:
| Time $(s)$ | Concentration of reactant $A$ $(mol \ L^{-1})$ |
| :--- | :--- |
| $0$ | $0.1$ |
| $15$ | $0.05$ |
| $20$ | $0.1 - x$ |

For a zero-order reaction,the correct expression for rate constant $(k)$ at half-life time $(t_{1/2})$ is ($[R_0] =$ initial concentration of reactant).

What is the correct relation between rate constant and half-life for a zero order reaction?

The rates of a certain reaction $(dc/dt)$ at different times are as follows:

Time $(sec)$	Rate $(mole \ litre^{-1} \ sec^{-1})$
$0$	$2.8 \times 10^{-2}$
$10$	$2.78 \times 10^{-2}$
$20$	$2.81 \times 10^{-2}$
$30$	$2.79 \times 10^{-2}$

The reaction is:

For a zero order reaction $A \longrightarrow \text{product}$,consider the following graph:
Where $[A_t]$ is the remaining concentration of reactant $A$ at time $t$. Calculate the concentration of $A$ after $2 \ s$. (in $mol/L$)