Question 469372
We want the least positive integer such that

{{{2^x > 15 * 10^22 = 1.5 * 10^23}}}

taking common logs of both sides, we get

{{{x*log2 > log1.5 + log 10^23 = log1.5 + 23}}}

<==> {{{ x > (log1.5 + 23)/log2 = 76.9893}}}

==> let x = 77.  Hence after the 77th minute.