After Jamal adds $x$ purple socks, he has $(18+x)$ purple socks and $6+18+12+x=(36+x)$ total socks. This means the probability of drawing a purple sock is $\frac{18+x}{36+x}$, so we obtain $$\frac{18+x}{36+x}=\frac{3}{5}$$ Since $\frac{18+9}{36+9}=\frac{27}{45}=\frac{3}{5}$, the answer is $\boxed{\textbf{(B) }9}$.

1. Jamal initially has 6 green socks, 18 purple socks, and 12 orange socks. Therefore, the total number of socks initially is:
$$6 + 18 + 12 = 36$$

2. Let $x$ be the number of purple socks Jamal added. After adding $x$ purple socks, the total number of socks becomes:
$$36 + x$$

3. The number of purple socks after adding $x$ purple socks is:
$$18 + x$$

4. According to the problem, the probability that a randomly selected sock is purple is now 60%. Therefore, we can set up the following equation:
$$\frac{18 + x}{36 + x} = 0.60$$

5. Converting 60% to a fraction, we get:
$$\frac{18 + x}{36 + x} = \frac{3}{5}$$

6. Cross-multiplying to solve for $x$:
$$5(18 + x) = 3(36 + x)$$

7. Expanding both sides:
$$90 + 5x = 108 + 3x$$

8. Subtracting $3x$ from both sides:
$$90 + 2x = 108$$

9. Subtracting 90 from both sides:
$$2x = 18$$

10. Dividing both sides by 2:
$$x = 9$$

Therefore, Jamal added $\boxed{9}$ purple socks.