We should find the equivalent ratios of 2:3:5:7 and then add the numbers together to get a sum of 68. A unit rate of two: 4:6:10:14 = 24. A unit rate of three: 6:9:15:21 = 51. A unit rate of four: 8:12:20:28 = 68. Now we know that the length of each side is 8:12:20:28.