ANSWER
x = 9
EXPLANATION
From the question, we see that DE is the midsegment of the triangle ABC.
According to the Midsegment Theorem:
DE = 1/2 * AC
=> AC = 2DE
Therefore, we have that:
3x - 15 = 2 * 6
3x - 15 = 12
Collect like terms:
3x = 15 + 12
3x = 27
Divide through by 3:
x = 27 / 3
x = 9
That is the value of x.
