We need to use the formula:

A(t) = Ao*e^(-rt)

where A(t) is the amount remaining at time t, Ao is the initial amount, r is the rate of decrease, and t is the current time

Now, half-life = ln2/r

=> 5700 = ln2/r

=> r = ln2/5700

=> r = 0.000121604

So, using A(t) = Ao*e^(-rt), we have when t = 22800, and Ao = 10 grams:

A(t) = 10*e^(-0.000121604*22800)

......= 10*e^(-2.772588722)

......= 0.625 grams

if it takes light 9.4 years to reach us, it means the star is 9.4 light years away.2. A light-year is approximately 5.88 x 10 to 12 power miles. Estimate the distance from Earth to a star so far away that its light takes 9.4 years to reach us.

1 light year = 5.88 x 10^12 miles

=> 9.4 light years = 9.4 x 5.88 x 10^12 miles

=> 9.4 light years = 5.53 x 10^13 miles

so the star is 5.53 x 10^13 miles from Earth