75% of a first-order reaction Was completed in 32 minutes. When was 50% of the reaction completed

Let original amount, N0=100Since 75% completed, so final amount N=100−75=25As we know N0N=2n,    where n = number of half lives  10025=2n, 4=2n   or,    22=2n∴ n=2Since total time =n×t1/232 minutes =2×t1/2∴  t1/2=16 minutes