In each 1 gram, we have 1000 miligrams, that is:
1 g = 1000 mg
So, we can use rule of three to find the answer:
x ---- 3.65 g
1000 mg ---- 1 g
Thus:
[tex]\begin{gathered} \frac{x}{1000mg}=\frac{3.65\cancel{g}}{1\cancel{g}} \\ x=1000mg\cdot3.65 \\ x=3650mg \end{gathered}[/tex]So, we have:
3.65 g = 3650 mg