$6-2$ A second$-$order irreversible elementary reaction $2$A products is

carried out in a batch reactor. For a certain set of conditions, it

is found that it took $20$ min for a reaction to reach $60$ percent

completion. What would be the time required to reach the same

degree of completion if $($a$)$ the initial concentration of A were

doubled and $($b$)$ the reaction rate constant were doubled?