By Basic Proportionality Theorem:

If a line is drawn parallel to one side of a triangle to intersect the other two sides in distinct points, the other two sides are divided in the same ratio.

=

3x (7x — 4) = (5x — 2) (3x + 4)

21 x² – 12x = 15x² + 14x – 8

6 x² – 26x + 8 = 0

3 x² – 13x + 4 = 0

3 x² – 12x – x + 4 = 0

3x(x - 4) – 1(x - 4) = 0

X = 1/3, 4

Since x cannot be 1/3 so x = 4