WooCommerce Shipping Help

I am using WooCommerce store on my website. I need help configuring the best way to set up the shipping.
I have only three flat rate shipping costs/options. Which are:
1-3 Items: $3.50
4-9 Items: $6.00
10+ Items: $12.00

I am struggling to find a way to set this up so that when a customer places 4 things in their cart they are charged $6.00 for shipping, or if they only have 1-3 items they are charged 3.50, etc…

Any suggestions, help would be greatly appreciated 🙂