Option A: 3a
The distance of a point from the x-axis is its y-coordinate (ordinate). For A(4a, 3a), the y-coordinate is 3a.
Source: Chapter 7, Section 7.1
The key definition from Section 7.1: "The distance of a point from the x-axis is called its y-coordinate, or ordinate." For point A(4a, 3a), the ordinate is 3a. Note: distance is always taken as a positive value, so the answer is 3a (not –3a), assuming a > 0.