The antibiotic clarithromycin is eliminated from the body according to the formula:

A(t)=500e^-0.1386t

A is amount remaining of mg remaining in body after (t) hours the drug reaches peak concentration. How much time will pass before the amoun of drug in the body is reduced to 100mg?

This is as far as I've gotten....I don't think I'm even close.

100(t)=500e^(-0.1386(t))

-100 -100

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t=400e^(0.1386(t))

Thanks for any assistance