Michael,
You need enough solution to process 5 sheets of 8x10, however much that is. Each sheet of 8x10 is 80 square inches, and you want to develop 5 sheets at a time. 5 sheets * 6 mL/sheet of stock means you'll need a minimum 30mL of HC110 stock to develop your 5 sheets. You'll have to add water to it, of course, to give yourself enough volume of working solution to develop the 5 sheets in your Jobo, however much that is (your Jobo tank should tell you).