12
18
20
24
Assuming perpendicular movement of the ships, the separation distance is the hypotenuse: \[ (60)^2 = (2x)^2 + [2(x + 6)]^2 \] Simplified equation: \[ 3600 = 4x^2 + 4(x^2 + 12x + 36) \Rightarrow 3600 = 4x^2 + 4x^2 + 48x + 144 \Rightarrow 3600 = 8x^2 + 48x + 144 \] Rearrangement to standard form: \[ 8x^2 + 48x - 3456 = 0 \Rightarrow x^2 + 6x - 432 = 0 \quad \text{(division by 8)} \]
Utilizing the quadratic formula: \[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \] With parameters \( a = 1 \), \( b = 6 \), \( c = -432 \): \[ \text{Discriminant} = 6^2 - 4(1)(-432) = 36 + 1728 = 1764 \Rightarrow \sqrt{1764} = 42 \] Solutions for x: \[ x = \frac{-6 \pm 42}{2} \Rightarrow x = \frac{36}{2} = 18 \quad \text{or} \quad x = \frac{-48}{2} = -24 \] The positive solution is retained as speed cannot be negative.
\[ \boxed{18 \text{ km/h}} \quad \text{(Option B)} \]