pre_text: 21. Subsidiaries The advances given to subsidiaries were interest-free and unsecured with settlement neither planned nor likely to occur in the foreseeable future. The deemed investment in a subsidiary, Singtel Group Treasury Pte. Ltd. (“SGT”), arose from financial guarantees provided by the Company for loans drawn down by SGT prior to 1 April 2010. The significant subsidiaries of the Group are set out in Note 44.1 to Note 44.3.
table: Company
table: 31 March 2019 31 March 2018 1 April 2017
table: S$ Mil S$ Mil S$ Mil
table: Unquoted equity shares, at cost 14,259.7 13,676.4 11,001.2
table: Shareholders' advances 5,733.0 5,733.0 6,423.3
table: Deemed investment in a subsidiary 32.5 32.5 32.5
table: 20,025.2 19,441.9 17,457.0
table: Less: Allowance for impairment losses (16.0) (16.0) (16.0)
table: 20,009.2 19,425.9 17,441.0
question: Analyse this data from a financial earnings document. What is the average balance of the total across the 3 years?