When you see a ratio, look for common factors of the two numbers that make up the ratio. In this case 2 goes into both numbers: 12:14 is the same as 6:7.
Now we can reverse the process. This time we multiply the reduced ratio by other factors. For example, 3:
18:21 is also the same as 6:7.
You can make other ratios by multiplying the numbers by another common multiplier like 5:
And so on.