Two ships are moving along a line due east (Fig. P17.58). The trailing vessel has a speed relative to a land-based observation point of $v_{1}=64.0 \mathrm{km} / \mathrm{h},$ and the leading ship has a speed of $v_{2}=45.0 \mathrm{km} / \mathrm{h}$ relative to that point. The two ships are in a region of the ocean where the current is moving uniformly due west at $v_{\text { current }}=10.0 \mathrm{km} / \mathrm{h}$ . The trailing ship transmits a sonar signal at a frequency of 1200.0 Hz through the water. What frequency is monitored by the leading ship?