The equation would be: Amount left = A(0.5)^(T/138)
There will be about 73.98 micrograms left after 60 days.
To find the amount that is left after 60 days, we will just enter the initial amount and the number of days into the equation. Then, evaluate.
A = 100(0.5)^(60/138)
A = 100(0.5)^(0.435)
A = 100(0.7398)
A = 73.98