1. **State the problem:** Solve for $f$ in the equation $$3 = 2f + 15$$. 2. **Isolate the variable term:** Subtract 15 from both sides to get the term with $f$ alone on one side. $$3 - 15 = 2f + 15 - 15$$ $$-12 = 2f$$ 3. **Solve for $f$:** Divide both sides by 2 to isolate $f$. $$\frac{-12}{\cancel{2}} = \frac{2f}{\cancel{2}}$$ $$-6 = f$$ 4. **Final answer:** The value of $f$ is $$\boxed{-6}$$.