Smallest cube has a edge length of 6 inches. what are the lengths of the other cubes if the ratios of similarity to the smallest cube are 1.25, 4/3, 1.5, 7/4 and 2 respectively

The ratio of similarity is simply the number you multiply by to scale from one similar object to another. Since you've been told the smallest object has an edge length of 6 inches, just multiply each of the ratios by 6 to get the length of their edge. So 1.25: 1.25 * 6 inches = 7.5 inches 4/3: 4/3 * 6 inches = 24/3 inches = 8 inches 1.5: 1.5 * 6 inches = 9 inches 7/4: 7/4 * 6 inches = 42/4 inches = 21/2 inches = 10.5 inches 2: 2 * 6 inches = 12 inches