In light of the fact that once a child turns 18, they no longer qualify for a child support grant and a foster care grant, unless they are still enrolled in schooling, what total number of children (a) who previously received the grants have exited the system due to reaching the age limit in the period 1 January 2017 to 31 December 2021 in each province and (b) are expected to exit the child support grant and the foster care system in 2022 in each province?