Iodine - thiosulfate titration.

Nov 2019
In an experiment, I made up a mixture of 300ml of water and 25ml of cyclohexane (saturated with iodine). I then allowed 2 layers to form and took a 100ml sample of the aqueous layer and titrated against 0.02M thiosulfate. Before titration, 5ml of KI was added to catalyse the reaction. How do I calculate the concentration of iodine in the aqueous layer?