When all of the territory of the non-high school district is annexed to one or more districts, the funds remaining to the credit of the non-high school district and property of such district shall within 60 days be apportioned and paid by the county board of school trustees to the respective school districts to which non-high school territory has been annexed since May 1, 1945, on the basis of the assessed valuation of the non-high school territory annexed at the date of the annexation to the respective school districts.