In the accompanying diagram, tangent PA and secant PBC are drawn to circle O from point P. If
the measure of arc AC = 80° and the measure of
arc AB
= 60°, what is the m2P?

step-by-step explanation:

ending amount = beginning amount / (2^n)

where "n" = number of half-lives (or elapsed time / half-life)

ending amount = 50 mg / (2 ^10 / 5.3)

ending amount = 50 mg / (2 ^ 1.8867924528)

ending amount = 50 m / 3.6981210597

ending amount = 13.5203794557 mg

or about 13.5 mg remain

source:  

you meant circumference well the answer is:

17.27876 miles

area is 23.7583

the radius is 2.75 miles

hope this hmu if needed.