An inertial observer \(\mathcal{O}\) is midway between two sources of light at rest in her frame with the sources \(2 \mathrm{~km}\) apart. Each source emits a flash of light that reaches \(\mathcal{O}\) simultaneously. Another inertial observer \(\mathcal{O}^{\prime}\) is moving parallel to the line that passes through the light sources and inertial observer \(\mathcal{O}\). In her frame \(\mathcal{O}^{\prime}\) measures the time of each flash and finds that they are spaced \(10 \mathrm{~ns}\) apart in time. What is the speed of \(\mathcal{O}^{\prime}\) with respect to \(\mathcal{O}\) ?