You can put this solution on YOUR website!
12 - X
24 - 100
Consider them as such:
12 is to X what 24 is to 100
Cross multiply to get the value of X
In other words,the ratio of 12 to 24 is the same ratio of X to 100,that is half.
If the ratio was to change,the value of X would accordingly change also.
Hope this helps,
best of luck.