I am struggling with one thing in shipping classes and I haven't been able to find the answer on these forums

I am struggling with one thing in shipping classes and I haven't been able to find the answer on these forums. I would like to be able to add a fixed cost per additional item in the cart. eg. If someone buys one item the shipping cost is £2.95 If someone buys 2 items, the cost is £3.95 (the shipping class amount plus a fixed amount for extra items) If someone buys 3 items, the cost is £4.95 (the shipping class amount plus 2 times the fixed amount for extra items) I hope this makes sense :?

via Chebli Mohamed