To get the ratio, we must pair up one side of a triangle to another side accordingly. In here, we can write the ratio of first side as 8:6. 8:6 can also be written as 8/6. we can simplify it as the common factor is 2, we will then have 4/3. The ratio of similarity is 4:3.
We can prove if its true by testing the other two sides as well. We will have 12/9 which has a common factor of 3 and 28/21 with a common factor of 7. if simplified, all sides has a ratio of 4:3