Chemical Kinetics

Consider a general first order reaction,

\(A(g) \longrightarrow B(g)+C(g)\)

If the initial pressure is 200 mm and after 20 minutes it is 250 mm , then the half-life period of the reaction (in minutes) is ( $\log 2=0.30, \log 3=0.48, \log 4=0.60$ )