The ratio shown in fraction form would be;

Now to convert it to its simplest form, you need to find their greatest common factor; (so in this case it would be 28...cause 28 goes into 56 evenly)
*Now divide both terms by
28
28 ÷ 28 =
1
56 ÷ 28 =
2
so your ratio 28 to 56 in simplest form is..

Hope this helps :)