You are given the following development triangle and ending case estimates: (a) Using the development method with all-year arithmetic average age-to-age factors, calculate the total reserve that should be carried for accident years 2020 to 2023 as of December 31, 2023. You can assume that the case estimates for 2019 and before were adequate and settled before December 31, 2023. (b) What additional data do you need to determine the IBNR reserve required at December 31, 2023