Activity of 10.0 mCi?

Question

1 curie of radiation is equal to 3.7 x 10^10 decay events per second (the number of decay events from 1 g of radium in 1 s)

What mass of Na(2)38-SO4 has an activity of 10.0 mCi? Sulfur-38 has an atomic mass of 38.0 and a half-life of 2.87 h.

I am completey confused on this one, I cant find an example in my textbook either,Any ideas or an equations i should use

Answer 1

10 mCi means 3.7 x 10^8 dps

Thus mass of S-38 = 2.87x3600x3.7x10^8x38/(0.693x6.023x10^23)
= 0.3479 nanogram

Thus, mass is 0.3479*125/38 = 1.144 nanogram