At 11:37 and at 12:24 you posted the same question
the earlier one was answered correctly by drwls by accepting your question the way you typed it.
my solution is based on the assumption that your denominator was e^(t-7), an invalid assumption.
the earlier one was answered correctly by drwls by accepting your question the way you typed it.
my solution is based on the assumption that your denominator was e^(t-7), an invalid assumption.