How to find the mass of a compound given the half life and activity?

[ununseptium]

Homework Statement

What mass of Na2 SO4 has an activity of 10.0 mCi? Sulfur-38 has an atomic mass of 38.0 and a half life of 2.87h

Homework Equations

Half life= 0.693/ k

Rate= kN

The Attempt at a Solution

I'm not sure where to begin the sulfur-38 part is throwing me off
All I need is some hint as to where to begin

 

[Borek]

What 10 mCi means?

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methods