Answer:
You´d need 9 1/2 of sugar
Explanation:
To solve this you just need to do a simple rule of three, where you know that you need to use 3 1/6 cups of sugar for every 2 4/6 of flour, so how many cups will you need to cook 8 cups of flour?, so you arrange the data the next way:

So you get that you will need 9 1/2 cups of sugar for the 8 cups of flour keeping the ratio of 3 1/6 of sugar for every 2 4/6 of flour.