How would I work this first-order reaction to find the half-life?

A certain first-order reaction A -%26gt; B is 25% complete in 16 minutes at 25C. What is the half-life of the reaction?





The answer is 39 min. I just need to know how to work the problem.How would I work this first-order reaction to find the half-life?
N/N0 = e^-kt


0.75 = e^-k(16)


Ln(0.75) = -k(16)


k = - Ln(0.75) / 16


k = 0.01798





for t(1/2), N/N0 = 0.5


0.5 = e^-(0.01798)t


Ln(0.5) = - (0.01798)t


t = - Ln(0.5)/(0.01798)


t = 38.6 minHow would I work this first-order reaction to find the half-life?
ln [A]f / [A掳] = - kt


t = 16 x 60 = 960 s


ln 75 / 100 = - k x 960


0.288 / 960= k


k = 0.000300





t1/2 = ln 2 / k = 0.693 / 0.0003=2310 s =%26gt; 39 min

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