Polonium is a radioactive element with the property that every 138 days the mass of the element in a sample reduced by half. (it's half life is 138 days.)
the rest of the question is in the picture.

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