**Step 1 — Recall the rule.**
For a point $P(x, y)$ :
- distance from the **x-axis** $= |y|$
- distance from the **y-axis** $= |x|$

**Step 2 — Identify the coordinates.**
For $A(4a,\ 3a)$ : $x = 4a$ and $y = 3a$.

**Step 3 — Apply the rule.**
$$\text{Distance from x-axis} = |3a| = 3a \quad (\text{taking } a > 0)$$

**Answer : (A) 3a**