The answer is 25 mcg.
Let's first convert units.
1 g = 1000 mg
0.015 g = x
Make the proportion:
1 g : 1000 mg = 0.015 g : x
x = 0.015 g * 1000 mg : 1 g
x = 15 mg
Therefore, 0.015 g = 15 mg
Now make the proportion:
15 mg contains 25 mcg.
15 mg contains x.
15 mg : 25 mcg = 15 mg : x
x = 15 mg * 25 mcg : 15 mg
x = 25 mcg
