Answer:
x = 12
Explanation:
In similarity triangles angles are congruent.
∠D = ∠A
x² - 8x = 48
x² - 8x - 48 = 0
x² + 4x - 12x - 48 = 0
x(x + 4) - 12(x + 4) = 0
(x +4)(x - 12) = 0
x - 12 = 0 {Ignore x + 4 = 0, as measurements won't have negative values}
x = 12