What is the time required for completion of $90 \%$ of a first order reaction?

For a first order reaction,show that the time required for $99 \%$ completion is twice the time required for the completion of $90 \%$ of the reaction.

What is the value of the rate constant for a first-order reaction if the slope for the graph of rate versus concentration is $2.5 \times 10^{-3}$?

The half-life of a first-order reaction is $1 \text{ hour}$. What fraction of the reactant will remain after $3 \text{ hours}$?

The rate constant of a reaction is $0.693 \times 10^{-2} \ min^{-1}$. What is the half-life period (in $s$)?

$A$ flask is filled with equal moles of $A$ and $B$. The half-lives of $A$ and $B$ are $100 \, s$ and $50 \, s$ respectively and are independent of the initial concentration. The time required for the concentration of $A$ to be four times that of $B$ is $.... \, s.$
(Given : $\ln 2 = 0.693$ )