The ratio of 3.5 chicken stock to 8 mixed veggies is:
3.5 : 8
We can simplify it a little bit:
1.75 : 4
Or even more:
0.875 : 2
Further on:
0.4375 : 1
We can also get rid of decimals by multiplying both sides of the base ratio by 2:
3.5 : 8 = 7 : 16
Just pick whichever ratio you like :)