Check each ratio by simplifying or comparing cross-products with the reference ratio 2:3.<br><br>
&bull; 4:6 ÷ 2 = 2:3 → equivalent ✓<br>
&bull; 6:9 ÷ 3 = 2:3 → equivalent ✓<br>
&bull; 8:12 ÷ 4 = 2:3 → equivalent ✓<br>
&bull; 12:20 ÷ 4 = 3:5, which is not 2:3 → NOT equivalent &cross;<br><br>
Final Answer: 12:20