For a three-term ratio to be equivalent, all three terms must be multiplied (or divided) by the same factor.<br><br>
&bull; 6:14:10 = 3×2 : 7×2 : 5×2 → equivalent ✓<br>
&bull; 15:42:25: 15 = 3×5, but 42 &ne; 7×5 (=35) and 25 &ne; 5×5 (=25...wait 5×5=25 ✓ but 7×6=42). Inconsistent factors (5, 6, 5) → NOT equivalent &cross;<br>
&bull; 18:42:30 = 3×6 : 7×6 : 5×6 → equivalent ✓<br>
&bull; 12:28:20 = 3×4 : 7×4 : 5×4 → equivalent ✓<br><br>
Final Answer: 15:42:25