Lead is found in Earth’s crust as several different lead ores. Suppose a certain rock is 38.0% PbS (galena), 25.0% PbCO₃ (cerussite), and 17.4% PbSO₄ (anglesite). The remainder of the rock is composed of substances containing no lead. How much of this rock (in kg) must be processed to obtain 5.0 metric tons of lead? (A metric ton is 1000 kg.)