Let a = kg of Alloy A, b = kg of Alloy B.<br>
a + b = 15<br>
600a + 800b = 720 × 15 = 10,800<br><br>
Substitute b = 15 − a:<br>
&bull; 600a + 800(15 − a) = 10,800<br>
&bull; 600a + 12,000 − 800a = 10,800<br>
&bull; −200a = −1,200<br>
&bull; a = 6, b = 9<br><br>
Check: 6 kg of A at $600 + 9 kg of B at $800 = 3,600 + 7,200 = 10,800. 10,800/15 = 720. ✓<br><br>
Final Answer: A = 6 kg, B = 9 kg