Answer is 12:21. How I got that answer is by making a bar diagram by drawing 4 3s at the top and 7 3s below. Then you should multiple the 3s, so on top you should have 3 times 4 equals 12, and the bottom is 3 times 7 equals 21. Then to the equivalent ratio you should divide the ratio 12:21 by 3 and you should get the ratio of 4:7