Question 852103
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Hi,
{{{I(t) = I[0] e^(-kt)}}}  0r  {{{I(t)/I[0] =  e^(-kt)}}} 
Finding 'k' first
 .5 = e^(-7.2k)
{{{ln(.5)/(-7.2)}}} = k = .0963
 .3 = e^(-.0963t)
{{{ln(.3)/(-.0963)}}} = t